Use ellipsis in menu items requiring further user input

[b4n]

This is a very common paradigm used by GNOME, KDE, MacOSX, Windows, etc., and following it makes our UI more consistent with these and easier to use by their users. As Geany itself follows this now (since geany/geany@9652a34, 1.24), it also makes plugin UIs more consistent inside Geany itself.

There is already a PR for project-organizer: #243.

I tagged with plugins that seem to have issues with this, but I might not have found all of them, and I may have misinterpreted some of them (unlikely, but who knows).

[b4n]

See also #248.