Add toolVersion block in to Gradle code sample to prevent errors.

Change file mode on `gradle` to be executable (nus-cs2103-AY1920S1#9)

Gradle defaults to an empty stdin which results in runtime exceptions
when attempting to read from `System.in`. Let's add some sensible
defaults for students who may still need to work with the standard
input stream.

Add configuration for console applications

This reverts commit cb85e8d.

adding Gradle to project

requires further implementation with regards to testing (JUnit)

# Conflicts:
#	src/main/java/Duke.java
#	src/main/java/command/DeadlineCommand.java
#	src/main/java/command/DeleteCommand.java
#	src/main/java/command/DoneCommand.java
#	src/main/java/command/EventCommand.java
#	src/main/java/exception/DukeException.java
#	src/main/java/main/Storage.java
#	src/main/java/main/UI.java
#	src/main/java/task/Event.java
#	src/main/java/task/Todo.java

# Conflicts:
#	src/main/java/main/UI.java
#	src/main/java/task/Task.java

To be implemented:
Full support of all Duke's previous features with the new GUI

…s in Main directory follow the CheckStyle. (#5)

Assertion checks to ensure that the correct types of command are passed as inputs.

Please note that all refactoring had already been done prior to this commit, incrementally.