Refactor the shortcut management for plugin macros

When saving a macro, a shortcut is created and the user can change the
shortcut in Options->Keyboard.
When the macro is removed, the shortcut is removed from the
actionManager using the removeShortcut method.
This is way simpler than before, where a number of default shortcuts
where defined and macros took the empty space.

Merge-request: 236
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>