Return content type and a json response in the case that an invalid database name is passed.  After this change more tests in the cblite-tests/cbl-database.js are passing.  Refactoring postponed for now.
The cblite-tests/cbl-database.js was failing when trying to create a duplicate db that already existed, because LiteServ was not returning a json with a status code.
Was ignoring the keys POST parameter, now it uses that to filter the all_docs response.  Fixes #147

https://github.com/couchbase/couchbase-lite-android/issues/147