Accels scm file - Allow for more than one shortcut to be assigned to an action

I noticed that actions generated in the "accels.scm" file can only have one hotkey assigned to them.
Suggesting to allow for more than one hotkey for more commonly used actions.

EXAMPLES OF ACTIONS TO OFFER MORE THAN ONE HOTKEY FOR

Next / Previous Image
This one I would allow for three hotkeys to be assigned for each, which Ristretto already uses three sets.\

Left = Previous Image
Right = Next Image

Up = Previous Image
Down = Next Image

Page Up = Previous Image
Page Down = Next Image

Currently only the Page Up/Down versions show up in accels.scm file to be customized
Currently the arrow key sets are hard coded as mentioned here #137 I would make these hard coded arrow key sets appear in accels.scm file instead, so user can have access to all three sets to customize. This would also make the arrow keys available to be used for other actions if user desires.

Back / Forward
Could benefit from two sets but maybe not important, this is similar to Next/Prev Image
Currently only has one set
Space = Forward
Backspace = Back

Zoom
Nice to have two sets for these.
Have seen some image viewers offer Minus and Plus keys but also up and down arrows for zoom action which I like
Zoom In
Zoom Out
Zoom 100%
Zoom Fit

Rotate
Maybe rotate could be useful to some users

Close Application
Also nice to have two for this action just for quick closes
Can use "X" "Q" "Escape"

I will stop there, but if any other users have any other actions to mention, please do so.

Thank You

If this update does get added, I would also see the following post about applying some kind of order to accels.scm file #139 (closed)