appDisplay: Properly check for TerminalEmulator in the Categories key

appDisplay: Properly check for TerminalEmulator in the Categories key

get_categories() returns an unparsed string, not a list of categories.
We need to parse the list by splitting on ';' to deterine whether the
actual 'TerminalEmulator' category is in the list, rather than something
like 'X-GNOME-TerminalEmulator'. It's an edge case, but I need to split
the list properly for the new folders, so I might as well fix this.

https://bugzilla.gnome.org/show_bug.cgi?id=723179