Little renewal of PurplePluginAction

[Tomasz Wasilczyk]

Hi,

I would like to take advantage of 3.0 in another aspect, where we can
break API: PurplePluginActions. I think, there is a need for these
improvements:

- possibility to create sub-menus, to group and hide not-so frequently
used, but useful features (like import/export);
- check menu items, for per-session (not per-account) boolean prefs
(like "show my current status only to buddies");
- possibility to temporarily disable an action (in case, when some
feature isn't accessible in certain moment).

Maybe something more? Please comment.

Tomek