Fix multiple design issues in this component

* SQL building code is now in classes that just build SQL
* Added MWQueryInterface builder to not force users to know about private construction logic
* Put MediaWiki specific code into MediaWiki sub namespace
* Added extra tests for table creation SQL building code
* Added usage and structure docs to README

Change-Id: I0cc82d12e80495d75fd810820c6527ba410affdd
Merge "Fix multiple design issues in this component"