Parameter --head=... now works together with --set-* switches

The parameter --head was ingorned when using the --set-* switches. It is now
possible to select a xinerama head by using the --head parameter.
Remove xinerama compile flags where not appropriate for --head support
Done Russian translation for nitrogen
Merge pull request #24 from vmax/russian-translation

Russian translation for nitrogen
WIP major refactor of SetBG statics into factory based approach
Fixed set_bg_once
Remove unneeded Util::restore_saved_bgs
Remove unused static setbg methods
WIP: finished refactor of setbg into base w overrides
Removed unused bits from restore refactor
Removed long set_bg overrides
Merge remote-tracking branch 'mbp/setter_refactor' into setter_refactor

Conflicts:
	src/SetBG.h
Fix compiler/runtime bugs
Determine which setter to use at runtime

This can be overridden by using --force-setter on the command line
to be one of "xwindows", "xinerama", "gnome".
Fix comparisons for --force-setter argument
Modernize gnome setter to use GSettings
Use bgsetter in main window to determine UI for select boxes
Add a desktop file (Closes: #28).
Update AUTHORS
Follow the Freedesktop spec for thumbnail location

According to the Freedesktop specifications for thumbnails [1], the
thumbnails directory should be stored in $XDG_CACHE_HOME/thumbnails, not
in $HOME/.thumbnails. This fixes that

[1]: http://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#DIRECTORY