Remove direct inclusion of headers

Superfluous in GTK+2, and forbidden in GTK+3
Stop use of deprecated symbols

Deprecated (but still working) in GTK+2, not working in GTK+3
Switch gtk2 to gtk3
Add start of C++ eid-viewer
Updates
Add gettext to the picture
Add support for threading, and an initial C_WaitForSlotEvent code
Make part of the license text translatable
Fix text so it is in line with current implementation
Cosmetic change: make sure the label is aligned properly
Implement translation logic
Don't forget to add the gettextize output
Create an accel group. Not quite working yet, though.