Move tabs and groups por Jackson McKay

Shortcuts:
Move tab left: Alt + Shift + Left
Move tab right: Alt + Shift + Right
Move tab group left: Alt + Shift + ,
Move tab group right: Alt + Shift + .

Mac shortcuts:
Move tab left: Cmd + Control + Left
Move tab right: Cmd + Control + Right
Move tab group left: Cmd + Control + ,
Move tab group right: Cmd + Control + .

The following shortcuts also exist but don't have a default keybinding:
- Pin/Unpin tab
- Ungroup tab
- Move tab to the next window
- Move tab to the previous window
- Move tab group to the next window
- Move tab group to the previous window

All shortcuts can be assigned/reassigned in Firefox by going to about:addons and selecting "Manage Extension Shortcuts" from the settings cog.

Notes:

If a tab runs off the edge of the screen, it wraps back around to the start.

Pinned tabs are fully supported.

If an ungrouped tab is moved around:
- with the single tab shortcuts, it will naturally join and unjoin tab groups as it runs into them
- with the tab group shortcuts, it will skip around any existing tab groups