Refactor common gradle logic into top level build script

Gradle was updated to version 1.0.0. If using the gradle wrapper, you
may need to update gradle/wrapper/gradle-wrapper.properties 'distrobutionUrl'
to version 2.2.1.
Set support library to version 21.0.2

Resolving the "unpredictable builds" warning in the gradle scripts.
Resolve "silly assignment" inspection warning
Merge pull request #9 from mdrabic/task/clean-up-gradle-scripts

Gradle Script Cleanup