* currently there are two ways to access default values:
OCP\Defaults or OC_Defaults (which is extended by
OCA\Theming\ThemingDefaults)
* our code used a mixture of both of them, which made
it hard to work on theme values
* this extended the public interface with the missing
methods and uses them everywhere to only rely on the
public interface
Signed-off-by: Morris Jobke <hey@morrisjobke.de>
