Updates for build.gradle and tested proguard/multidex

- Updated `buildToolsVersion` in `build.gradle`
- Updated `com.android.tools.build:gradle` in `build.gradle`
- Updated Gradle `wrapper`
- Added `proguardTest` to `buildTypes` enabling Proguard with `minifyEnabled` and `shrinkResources` which verifies: http://stackoverflow.com/questions/26024694/how-to-successfully-obfuscate-project-with-dagger-2-0-using-proguard
- MultiDex does not work with Dagger 2.0 example producing errors:
`java.lang.NoClassDefFoundError: dagger.internal.MembersInjectors` and `java.lang.NoClassDefFoundError: dagger.a.b`

This whole task is not needed. Once the wrapper has been checked in you can just edit the properties file to update it.