Base-Class Support for meta model, database reset and type based query

Added support for derived classes from a specific base class, allows to
reset the database from code and added a query method which returns all
models of a specific type
Merge pull request #1 from dei79/small-improvements

Base-Class Support for meta model, database reset and type based query
fixed migrator so that it ingores the fields it should when migrating
created class which implements IScriptFile and can be used for registering custom SQL with MODbMigrator
updated readme to reflect new requirements
moved test db file from MiniORM group to ObjCMiniORMTests group where it belonged
There's no need for the migrator to require an open connection. If the connection is not opened, a call to open will open it. If the connection is already opened, a call to open will do nothing
set database variable to NULL for clarity
MOScriptFile now supports multiple sql statements. Use MOScriptFile for testing instead of separate test file
added more helper methods for querying
make query support parameters
added helper queries that return a single record
need to make sure connection is open before attempting to create script history table