update submodules
Change it to call "gradle assemble" rather than "gradle build"

When calling "gradle build", it tries to run tests for the portable java projects like couchbase-lite-java-javascript, which fail because they don't have a storage engine.

http://www.couchbase.com/issues/browse/CBLT-237
add mkdir() command get the build_android_artifacts.sh working locally.

While trying to get the build_android_artifacts.sh script working locally, I found that it was giving errors because the directory didn't exist so it couldn't copy jars into it.  The script seemed broken, so I made a small change to have it mkdir() that directory.

http://www.couchbase.com/issues/browse/CBLT-237
1) Add couchbase-lite-java-core.  2) Look in different place for jars.

Now that some of the projects are pure java, they put their jars in a completely different place.  I updated the script so that it looks for them in the right place.

Also, it was completely ignoring the couchbase-lite-java-core jar, which is essential for any working system.

http://www.couchbase.com/issues/browse/CBLT-237