Build -source.jar and -javadoc.jar

Downgrade Android Gradle plugin to 0.5.4 to allow referencing android tasks
from publishing plugin. This does not work in 0.5.5.

Downgrade Gradle version to 1.6 to meet requirements of Gradle Android 0.5.4.

Fix malformed @link directive in JsonUtil javadoc.
Fill required POM metadata, version is -SNAPSHOT

Modify publishing configuration to fill all metadata required by
Sonatype/MavenCentral.

Modify version to -SNAPSHOT. Release packages will be created via
Jenkins/Artifactory promotion.