Remove unnecesary files to reduce library size and fix gradle settings

Size change of ColoursLibrary/build/libs/ColoursLibrary.aar

Before: 39190
After: 8179

79% less and happy face :-)

Test Plan:
1. ./gradlew clean installDebug
2. run the sample app
Merge pull request #3 from frankdu/size_and_gradle_fix

Remove unnecesary files to reduce library size and fix gradle settings