Simplified by removing Filters

We now have a basic Filter that contains a Provider and a set of parameters. The
parameters should match the documentation of the respective provider.
README fix
Refactoring

(sorry)

-   Removed some unneeded files
-   Restructured filters - in most cases a custom Filter class is not needed,
-   Simplified config (untested)
Fix tests/missing implements
Rename test
Add defensive test when CloudImage has no transformer set
Merge pull request #6 from rmasters/simplification

Refactoring