Language Pack DB schema and object model

Added Language Pack DB schema and object model.
Added tests for Language Pack schema.
Added language pack attributes.
(compiler_versions, language_impl and os_platform are added as columns,
other attributes are added as a json blob in the language_pack table.)
Added service.id as foreign key in language pack table.

Change-Id: I95aec95e47d2aa5662471122a553d916e5b0b4b3