[rfe] add possibility to remap F1 keymap
Please unhardcode F1 key. Right now to do it user has to make a lot of toil (I've just published the way how to do it in my blog https://skobki.com/gimp-bind-f1/ ; it's in Russian).
It's pretty important.
Help is no use really in google times.. And F1 is one of the most often used hotkeys. I've just migrated from Photoshop to GIMP and was pretty amazed that in PS it's possible to do this simple thing (map anything to F1), while in GIMP it's doable only via config files :E