#513 [lxlauncher] Workaround for invisible icons on GTK+ 3

[Balló György]

This patch is a workaround for invisible icons on GTK+ 3. I think it's a bug in the ExoWrapTable implementation, because the app buttons are added to the table, but their size is zero.

• Fix background drawing on GTK+ 3.
• Button label size hack is not needed on GTK+ 3.
• Disable monitoring changes in menu on GTK+ 3, as it currently causes invisible icons.

[Lonely Stranger]

The issue with invisible icons requires a better solution, because disabling update is very wrong, users who installed/removed/changed applications will never see any changes without session restart, which is pretty much weird, really. I'm not ready to make any researches in that GTK+3 behavior right now so would like to not touch it yet. Thank you very much, anyway.

[Balló György]

Okay, I opened a bug instead:
https://sourceforge.net/p/lxde/bugs/803/