[patch] Effect preview in awn-manager

[Matt]

Inspired by http://awn.planetblur.org/index.php?shard=forum&action=g_reply&ID=2032&page=1&isLive=true#23816 I have implemented this idea. A preview widget shows up to the right of the effects section. Unfortunately, it significantly increases awn-manager's startup time, by about a second. Maybe a "Show Preview" button could be included?

Note that glade-3 decided to change a thing or two that it shouldn't, so I adjusted the code a bit.

[Matt (mjz)]

Screenshot, of course!

[Michal Hruby (mhr3)]

Thanks for realizing the idea. ;)

A few comments:
1) try to load the pixbuf in the constructor, not every time in the expose event.
2) expose method should "return True" on the end - I think these two should solve the prolonged loading issue.
3) use "self.effects.set_offset_cut(False)" to fix the clipping issue when using 3D look.
4) when requesting size use width*5/4, so zoom and squish effects works ok.

Also it'd be great to preview the opening/closing etc effects - perhaps this could be done when changing respective effects while using "Custom" icon effects?