Update README per issue #17

https://github.com/couchbase/couchbase-lite-java/issues/17
Add java-native submodule
Update submodule
Update build.gradle

Update build.gradle to compile libraries/couchbase-lite-java-native submodule
Update build.gradle and add scripts for jenkins build
Update submodule
Update README.md

Added a note for building on Mac OS X, Xcode command line tools must be installed otherwise uni.h header files are not available
Update README.md
Merge remote-tracking branch 'upstream/master'

Conflicts:
	build.gradle
	gradle/wrapper/gradle-wrapper.properties