Draft: Port to GTK3

Hi,

So this is a base. I'm sorry I haven't done much due to personal issues and I had less time than I thought...

What I did :

• Adding a splash screen at the start of the application while searching for devices
• Adding the main window. There is not all the options since I have some questions...

here is some screenshot :

The splaschreen

the view when no devices was found:

When there is devices:

The main window:

Concerning the main window I wanted to see with you some things;

1. In sane there is SANE_NAME_BRIGHTNESS and SANE_NAME_CONTRAST but Xsane doesn't seems to use them (it uses a range -100 to 100). Is it because this options are inactives ? Do I have use this options ? If yes and this options are inactive do I use a custom range of -100 to 100 ?
2. My apologies but I didn't understand very well SANE_NAME_HIGHLIGHT/SANE_NAME_SHADOW... Is it used for the medium stuff ? It's available on all scanners right ...?
3. I thought about changing the list of buttons at the bottom of the window (rgb_default, etc). The main reason is that activating the rgb_default button the window may exceed the size screen. Here a screenshot to understand what I'm trying to say :

If we add buttons for scanning etc, we won't be able to see them at all...

4. The option to show the resolutions as a list, Is it really needed ?

5. The info window, does it have to be a window or it can be a dialog ?

6. I think I forgot some questions ...

For the tooltips I added them on the icons instead on the widget, I thought it makes more sense but maybe (surely) I'm wrong.

Also, I could not test for the x/y_resolution I didn't find any scanners with this options neither for with the auth callback...

Again sorry for this poor start, please let met know if you don't like what I did or if there is a problem.

Thanks