Using gradle build system.

The summary of import is listed below. Apart from that, the following changes were made:
* Using a customized gitignore file
* app/build.gradle updated to disable running proguard (needed for travis later)
* app/build.gradle update to disable aborting on error (needed for travis later)

In order to develop using this new build system:
* Download Android Studio here: https://developer.android.com/sdk/installing/studio.html
* Open the build.gradle file in Android Studio
* It will prompt you to "import" the project. This is a one-time step (unless you `git clean -fdx`). Press OK
* You are ready to go. Press Ctrl+R to build and run the app in the emulator

Import Summary:
ECLIPSE ANDROID PROJECT IMPORT SUMMARY
======================================

Ignored Files:
--------------
The following files were *not* copied into the new Gradle project; They were henceforth deleted

* .gitignore
* README.md
* app/
* app/src/
* app/src/main/
* app/src/main/res/
* app/src/main/res/drawable-hdpi/
* app/src/main/res/drawable-hdpi/icon.png.orig
* app/src/main/res/drawable-mdpi/
* app/src/main/res/drawable-mdpi/icon48x48.png.orig
* app/src/main/res/drawable-xhdpi/
* app/src/main/res/drawable-xhdpi/icon96x96.png.orig
* app/src/main/res/drawable/
* app/src/main/res/drawable/icon.png.orig
* app/src/main/res/drawable/icon24x24.png.orig

Moved Files:
------------
Android Gradle projects use a different directory structure than ADT
Eclipse projects. Here's how the projects were restructured:

* AndroidManifest.xml => app/src/main/AndroidManifest.xml
* libs/mongo-2.10.1.jar => app/libs/mongo-2.10.1.jar
* res/ => app/src/main/res/
* src/ => app/src/main/java/