Consider to deprecate 'fm_terminal_new()' in favour of 'gtk-launch'

[ghost]

Having a custom list of opening and closing arguments for every possible terminal seems an overkill to me, since some terminals like Wayland-based 'foot' use a double-dashed separator (optionally) as an opening argument instead, throwing an error.

If having an extra 'libgtk*-bin' dependency is a "no-no" — let user set a terminal emulator without default optional arguments, as an optimal solution.

Dyakuyu.