closing Lucide with ALT-F4 is only possible right after starting Lucide

[Robert Henschel]

When you double click the Lucide icon, or open a PDF document that is associated with Lucide, you can close Lucide with the keyboard by pressing ALT-F4. But this only works if you have not transfered focus inside Lucide to the document area. If the document area has the focus, you have to press CTRL-X to close Lucide (ALT-F4 will not work). If the menu or the navigation pane have the focus, you can also use ALT-F4 (and CTRL-X will also work).

I do not vote for one or the other keyboard shortcut, I just would like to have it consistent. (well, actually, I would like ALT-F4 to work in Lucide from everywhere ;-) )

[Eugene Romanenko]

(In [67]) fixed processing of syscommands when document area active (closes #41)