Fixed source directories in gradle build file

... and update of build tools and support library.
Added missing application tag in AndroidManifest.xml
Added Google Play Services to Gradle build dependencies
Merge pull request #44 from stuffle/fixed-gradle-build

Fixed Gradle build
New version v3.3.1
Merge pull request #46 from adjust/v3.3.1

New version v3.3.1
Updated pom for Google Play Services
Created Maven Google Play Services readme
Update version release
Merge pull request #48 from adjust/maven

Maven play services