docs(package.json): Add missing fields to package.json

Add `description`, `directories`, `repository`, `keywords`, `license`,
`bugs`, and `homepage`  fields to package.json

Add AUTHORS file, instead of providing `contributors` field in
package.json

AUTHORS

@@ -0,0 +1,6 @@
+# List of Authors, in the npm format:
+# Name <email> (url)
+Mathew Kallada (https://github.com/kallada)
+Glavin Wiechert (https://github.com/Glavin001)
+Joel Kuntz (https://github.com/Frozenfire92)
+Sarah MacDonald (https://github.com/rainbee2214)

package.json

@@ -40,5 +40,23 @@
   },
   "scripts": {
     "test": "grunt test"
-  }
+  },
+  "description": "Accessible and client-side threat modeling tool.",
+  "directories": {
+    "test": "test"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/mozilla/seasponge.git"
+  },
+  "keywords": [
+    "threat",
+    "modelling",
+    "tool"
+  ],
+  "license": "Mozilla Public License, version 2.0",
+  "bugs": {
+    "url": "https://github.com/mozilla/seasponge/issues"
+  },
+  "homepage": "https://github.com/mozilla/seasponge"
 }