Adding sontatype maven central configuration
Fixing pom issues

change packaing to aar
add name and update description

Missing name caused sonatype to fail the check
Check for properties before using

Allows building without them being present in gradle.properties
Don't assemble release for tests

Signing fails due to no gpg key
Merge pull request #139 from Simperium/feature/maven-publish

Maven Central/Sonatype configuration