Draft: gtk3 initial port

This is a preview of the gtk3 changes for extras. acquisition-server seems to work on my limited testing. I checked that the driver properties interfaces are working for all the drivers installed on my computer (i.e everything default + EEGO). Fully tested with EEGO. I'm fairly confident that it is working fine, but there is always the possibility that I missed something or that something is wrongly connected between Gui and the acquisition process itself. For plugins, I just tested the SignalViewer which mostly works (an annoying bug remains because the signal window is cleared when the window is entered or or leaved, but this is not due to the callbacks. Correction will come later). All the .ui files have been adapted to gtk3 (removal of {HV}{Box,Paned,Separator} and of GtkTable, occasional conversion of GtkComboBox to GtkComboBoxText). Other big changes, are the use of cairo for all drawings and the use of css styles instead of functions to change the window styles.

A big bug which puzzled me for a while was that the SignalViewer was not working at all initially. It was a hard-to-find bug which boiled down to classes with the same name bug differing content in extras and designer. Issue opened #85 . I DID NOT SOLVE THE FUNDAMENTAL PROBLEM, I JUST MADE THE TWO STRUCTURES COHERENT... I guess this problem will be better solved when Thomas will merge the trees...

As for the designer branch, I have not removed Stock icons and several other deprecated features in gtk3. Different bugs will be corrected, when I find them. Some of them are at the designer level. It also seems that some minor issues that were present on linux before are solved... These are mostly some information that was no longer correctly displayed (e.g. in the "window manager").

As for the designer case, this has been branched from master and not develop as I had to use my fedora changes. Sprry.