[Feature Request] Support for more key combinations

[alch-emi]

Currently, there exists no way to describe the following key combinations:

• Ctrl or Alt plus any non-character key (e.g. Ctrl+Right, Alt+Fn1, or Ctrl+Backspace)
• Shift as a modifier to any character which doesn't have a shifted variant on the users keyboard (e.g. Shift+Tab or Shift+Right)
• Combinations of Ctrl and Alt (and implicitly Shift) (e.g. Ctrl+Alt+f)

This poses an issue as these are common shortcuts used in many applications, and requests for features bound to these combinations by default have come up in numerous issues, thereby making this issue a prerequisite for

• #45, which requests Shift+Tab as a binding to move a node up a level
• #61, which requests Shift+Direction as a shortcut to pan the view (opened by me)
• Likely #15, which doesn't specifically request any shortcuts, but due to the innate directionality of the request, would likely need to be bound to arrow keys + a modifier, or use some sort of modal control such as in #58