XBM icon support

<icon=/path/to/icon>
Some tabs slipped in, reindent
Add finalizer for the icon pixmap
reindent again
Implement icon caching
Move bitmap functions into Bitmap module
Fixes for previous
<icon=..> -> <icon=../>
Add standard header
Fit to 80 columns
Slight hlinting
A bit of documentation and credits for Edward and Alexander
Remove unsafe fromJust from Volume plugin
Removing uneeded uses of hiding (catch)
Handle XReadBitmapFile errors
Use real icon width
Better icon alignment
Allow icons in monitor templates
readBitmapFile was included into X11 package
Delay as much as possible setting window properties