Split the save keyboard shortcut into save and saveRES

Suggested in #417.

This does change existing behavior (the save key now saves comments to reddit instead of saving them to RES, which now has its own key), but I think most users who are smart enough to save posts to RES should be able to figure out the new shortcut.

This also allows the save-RES status to be toggled before a refresh (i.e. you click `save-RES` and it becomes `unsave-RES` and can be toggled, but after a refresh it becomes `saved-RES` and you must go to the saved page to delete it), which I think is a fair balance: users can easily unsave something if it was an accident, but can't accidentally unsave something that they are revisiting.