add an apdapter map

this permits wrapper classes to automatically map scheme to an adapter
add adapter map for CakePHP datasources

Right now only populated with core datasources, all cakephp/datasources
classes should be added to this list - as well as any other
defacto-standard datasources.
add a test for using the map function
Merge pull request #3 from AD7six/feature/adapter-map

Add an adapter map