Finish migration to have one plugin loader for flake plugins.

Each plugin will have a KService factory only one time and it can now choose from being a Shape-only plugin, a Tool-only plugin or to be a plugin of type "KOffice/Flake" which can contain both types.

This solves the weirdness that if you had both a shape and a tool you had to choose one and do some magic in the constructor to have the other type known as well.