VTE & Terminal requirement bumps

[Egmont Koblinger <egmont gmail com>]

Hi Release Team, (cc Christian,)

Not sure if you care about this or not (as per recent discussions on
desktop-devel-list), but let's stay on the safe side.

VTE bumped its requirements on master (0.59) to glib >= 2.44 and gtk >= 3.20.

(Also you probably noticed: the just-released stable 0.58 introduced
fribidi >= 1.0 as a new external dependency. It's optional, but
required to get BiDi support, the terminal's big new feature for gnome
3.34.)

gnome-terminal bumped its requirements on master (3.35) to glib >=
2.50, gtk >= 3.22.27 and nautilus >= 3.28.

The particular version numbers were chosen so that we could do a code
cleanup and get rid of previous #ifdefs.

cheers,
egmont