use the built-in AndroidContext to create the Manager object.
removed database proxy cache usage for now -- it causes a "java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase" error
restored database proxy cache and it seems to be working ok.
added tests for query methods
fixed old method name in createDocWithProperties()
004_all_docs_query unit test working on Android
005_database_validation unit tests passing; refactored some of the revision and validation classes.
clean up databases before test
006_document unit tests passing.  Changes include:

* added a document proxy cache to DatabaseProxy
* refactored the revision proxy class structure
* cache the current revision proxy in DocumentProxy
* fixed issues with type conversion in TypePreprocessor