Changes \GdWrapper\Action\Action interface.

* Method \GdWrapper\Action\Action::execute() now has 1 parameter: the
source image resource to apply the action. Previously, this was a
constructor parameter.
* Updates docs.
Changes \GdWrapper\Io\Writer interface.

* \GdWrapper\Io\Writer no longer knows \GdWrapper\Resource\Resource.
Instead, it now receives directly a GD2 image resource to work with.
Removes unused methods and property from AbstractResourceFactory.
Mutiple changes:

* Creates Crop action and its strategies
* Adds 'project' folder for UML diagrams
* Fixes AbstractResourceFactory