Fix gradle deploy

Fix for DeployGate/deploygate-android-sdk#2.

Changed pom to jar
Added JavaDoc and Sources to Artifact upload.
Updated version to 3.1

Updated to lastest BuildTools.
Updated to compile with api 19 (always build/compile the latest version)
Updated gradlew to 1.9 to support lastest build tools (Android Studio 0.4+)

Updated gitignore to ignore certain IDEA files.

If you happy, just merge and deploy to Maven again.