ResourcesCOnfigWindow: OpenAL sound devices recognition ready.

Merged with branch resources_config_window_win_compile.
Detection, selection and saving of sound device through OpenAL
is up and running (MantisBT issue #345)
We now force fullscreen mode, whatever configuration was chosen
(MantisBT issue #348)

TODO: fix loading of background image (MantisBT issue #346)
ResourcesConfigWindow: ugly fix to show widget background image.

FIXME: image must be in sub-(or same) directory than executable.
The proper way would be to use Qt resources system, currently not working!
ResourcesConfigWindow: removing unnecesary field from main class
Merge branch 'resources_config_window' into cordobazombie0.1