Summary: Removes hard requirement for xterm, which caused connection editing to fail.
Test Plan:
1. Right click on nm-tray
2. Click "Edit Connections"
If successful, qterminal will open, though the display will not be correct. Additional changes to lubuntu-default-settings are required, as described in the bug.
Reviewers: tsimonq2
Reviewed By: tsimonq2
Differential Revision: https://phab.lubuntu.me/D3
