Implement basic keyboard controls for manipulating edges

[cemulate]

Clicking the far away buttons for changing edge properties was driving me crazy!

I've implemented basic keyboard navigation for when you have an edge selected. If you have better ideas about what keys should be used, I'd love to hear them, but the basic idea is there.

I've renamed data in App to be a little more descriptive and match the corresponding stuff I added in Properties

[yishn]

Apologies for the delay. Here are some thoughts:

• I think it's better to handle keyboard shortcuts on keyup rather than on keydown accessibility-wise. The keyboard shortcut for 'Remove Arrow' is also in keyup; we should probably keep them in the same place.
• I'm not sure, but maybe the shortcuts for bending should be top/bottom arrows, aligning with the toolbar icons? What do you think?
• A, S, D for label positioning seem pretty random, but I have no better ideas either...
• We should hint the keyboard shortcuts in the tooltip of the toolbar buttons, just like I did with the toolbar buttons for the pan/arrow tool or 'Remove Arrow' button.

[cemulate]

No prob on the delay.

I like your idea about "up" and "down" considering that matches the icons. I've also moved all that I can to keyup. Unfortunately, the Enter to edit cannot be on keyup, since if you're editing the label the Enter press that triggers form submission does so on keydown which means you immediately open the edit label again on keyup (if you have a better idea to handle that, let me know).

My logic for the label movement just comes from using WASD as the left set of arrows - most peoples' hands will be resting there anyway, and it seemed like a natural choice for left-middle-right.

Just realized I forgot to hint the buttons, I'll do that real quick as well.

[yishn]

Thank you very much!