build.gradle: add javafx runtime dependency for all platforms

We have added the platform-specific javafx runtime dependencies, so the
addressbook is able to run locally.

However, the jar file generated on one OS cannot run on other OS. The
reason is that, after detecting the OS, javafx will try to load
platform-specific classes dynamically. Without corresponding javafx
dependencies for that other OS, the class loading process will fail.

Let's add the javafx runtime dependency for all platforms (MacOS,
Window, Linux) so the jar file generated on one OS is able to run in
other OS [1].

[1] https://stackoverflow.com/questions/52653836/maven-shade-javafx-runtime-components-are-missing/52654791#52654791

build.gradle

@@ -2,18 +2,8 @@
 // For more details take a look at the Java Quickstart chapter in the Gradle
 // user guide available at http://gradle.org/docs/5.2.1/userguide/tutorial_java_projects.html
 
-import org.apache.commons.lang3.SystemUtils
 import org.gradle.api.tasks.testing.logging.TestLogEvent
 
-buildscript {
-    repositories {
-        mavenCentral()
-    }
-    dependencies {
-        classpath group: 'org.apache.commons', name: 'commons-lang3', version: '3.8.1'
-    }
-}
-
 plugins {
     id 'java'
     id 'jacoco'
@@ -51,25 +41,29 @@ test {
     useJUnitPlatform()
 }
 
-String platform = SystemUtils.IS_OS_WINDOWS ? 'win'
-    : SystemUtils.IS_OS_LINUX ? 'linux'
-    : SystemUtils.IS_OS_MAC ? 'mac'
-    : null
-if (platform == null) {
-    println 'The current OS is not supported.'
-}
-
 dependencies {
     String testFxVersion = '4.0.15-alpha'
     String jUnitVersion = '5.1.0'
     String javafxVersion = '11'
 
-    implementation group: 'org.openjfx', name: 'javafx-base', version: javafxVersion, classifier: platform
-    implementation group: 'org.openjfx', name: 'javafx-controls', version: javafxVersion, classifier: platform
-    implementation group: 'org.openjfx', name: 'javafx-fxml', version: javafxVersion, classifier: platform
-    implementation group: 'org.openjfx', name: 'javafx-graphics', version: javafxVersion, classifier: platform
-    implementation group: 'org.openjfx', name: 'javafx-media', version: javafxVersion, classifier: platform
-    implementation group: 'org.openjfx', name: 'javafx-web', version: javafxVersion, classifier: platform
+    implementation group: 'org.openjfx', name: 'javafx-base', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-base', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-base', version: javafxVersion, classifier: 'linux'
+    implementation group: 'org.openjfx', name: 'javafx-controls', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-controls', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-controls', version: javafxVersion, classifier: 'linux'
+    implementation group: 'org.openjfx', name: 'javafx-fxml', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-fxml', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-fxml', version: javafxVersion, classifier: 'linux'
+    implementation group: 'org.openjfx', name: 'javafx-graphics', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-graphics', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-graphics', version: javafxVersion, classifier: 'linux'
+    implementation group: 'org.openjfx', name: 'javafx-media', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-media', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-media', version: javafxVersion, classifier: 'linux'
+    implementation group: 'org.openjfx', name: 'javafx-web', version: javafxVersion, classifier: 'win'
+    implementation group: 'org.openjfx', name: 'javafx-web', version: javafxVersion, classifier: 'mac'
+    implementation group: 'org.openjfx', name: 'javafx-web', version: javafxVersion, classifier: 'linux'
 
     implementation group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.7.0'
     implementation group: 'com.fasterxml.jackson.datatype', name: 'jackson-datatype-jsr310', version: '2.7.4'