Improve context menus and link opening by keyboard
- Made context menu items more closely match groups/ordering of
the File Explorer context menu - Support opening files to the right or in a new window via
Mod-Alt-Enter and Mod-Alt-Shift-Enter (as well as clicks,
which already worked) - Moved "Show in Quick Explorer" to the "system" menu group in
other context menus, where it will be grouped with "Reveal file
in navigation", "Show in system explorer", etc.