appDisplay: Special case terminal launching

One of the most frequent complaints about our launching behaviour is
how we handle terminals. Among all MDI applications, the terminal is
the one that is most likely to have lots of semi-independent windows
opened at the same time, and spawning new windows is much more common.
More so, if it does not support tabs.

Therefore, we special case terminal launchers to always create a new
window. It is an application that most non-technical users will not
use, so chances of them being confused by any special behaviour is
expected to be low.

https://bugzilla.gnome.org/show_bug.cgi?id=695010