JuliaGraphics
add basic GtkClipboard support
It's the first time I do this, I hope I didn't messed up somewhere. I didn't added short names because there's already some clipboard methods in Base, but maybe it's not a problem.
clipboard_wait_for_text crashes when it's called from the terminal because Gtk checks for a main_loops that's not defined in that context, is there a way to check that from Julia to make it safer?
I tested it only on windows 7.
I couldn't find the value of the CLIPBOARD one anywhere so I generated the list by calling gdk_atom_name. Thinking about it it's probably not the best idea, these are maybe not constant.
Some are defined here though:
https://developer.gnome.org/gdk3/stable/gdk3-Selections.html#GDK-SELECTION-PRIMARY:CAPS
I can restrict them to this list. Otherwise I just saw there's gdk_atom_intern that allows to get the value at runtime, it's maybe safer.
