Update to work with vte 2.91 as well as 2.90
Merge branch 'iainlane-next' into next #372
GTK3 migration - GTK_STOCK deprecated + GTKGrid fixes #365
Remove unneded call to non existent function remmina_rdp_load_plugin, fixes #374.
Fix rdp_cliprd for freerdp 1.2. Fixes #378 #379

Also added support for DIBV5 bitmaps in clipboard.
Merge pull request #384 from giox069/next

Fix rdp_cliprd for freerdp 1.2. Fixes #378 #379
Removing deprecated GTK threading form rdp_plugin
Switched to GTK+3.6 threading model, make pthreads compulsory.

Many changes to call GTK/GDK functions only on main thread.
Now libphtreads is compulsory.
Moved GTK calls on main thread.
Other mt changes
rdp plugin changes
Removed THREADS_ENTER/EXIT from rdp_plugin