Change channel reorganization (move up/down) from `cmd-up/down` (mac) /
`ctrl-up/down` (linux) to `alt-up/down` (both) to match moving lines in
the editor.

Also fix an issue where if you selected channels using down/up in the
filter field, the movement shortcuts would not work (`editing` vs
`not_editing`).

Release Notes:

- N/A