GTK+ 2 compatibility

There were two problems when I tried to use Remmina on GTK+2:
* The Quick Connect bar was taking too much space, like half the height of the main window
* A segmentation fault right after the mouse pointer changes in a RDP session

The commit 6e4a0b6 contains the fix. I am a newbie with git and Github (git is still alien to me), this pull request is too large. Although you may be interested to some other changes like:
* a679e58 : Fixed Gentoo QA Notice in desktop file
* 0009c9f : Recompressed icons. Also removed executable bit to some icons.
* d3d2b41 : Corrected compile warnings