Use checkmarks instead of disabling items in the context menu

[Nodd]

Instead of disabling unavailable and the current checked item, only the unavailable actions should be disabled (like removal for a package not installed).the other options should be all enabled and the chosen option would be marked with a ckeckmark. By default, unmarked would be checked.
I think this will even simplify the code a little bit since you'll have less enable/disable to manage.

[goanpeca]

This is needed if we want to go along your other suggestion on not disabling items after having selected one option.

Not entirely convinced yet.

@Discalced51 what do you think?

[Nodd]

It's the other way out: not disabling items is needed for using checkmarks, but you can not disable items without checkmarks since the status is shown by the icon.