Drawing segment type toolbar item

[quincylvania]

Breaking this off from #5960: we should have a toolbar item while drawing to switch between normal (straight) and orthogonal drawing. The user could switch between them while drawing a feature, with the orthogonal segment relative to the previous segment. This would work for both lines and areas. See also #2699.

[quincylvania]

I did this! The orthogonal drawing is fairly primitive, but it gives us a place to start from. We should target the functionality shown in #2699.

[BjornRasmussen]

This is AMAZING! I just tried it out on preview.ideditor.com/master and love it!
I do have couple of suggestions, though:

• allow for 45, 30, & 60 degree angles:
  JOSM looks like this:
  
• snap to places where a previously added node in the way is 90 degrees to the right or left.
  JOSM looks like this:
  
  this makes it easier to end a way as a squared shape.

[BjornRasmussen]

JOSM also has a quick way to switch between the two drawing modes: pressing the keyboard shortcut A. This might also make sense in iD, since I find myself switching between the two modes a lot.

[quincylvania]

JOSM also has a quick way to switch between the two drawing modes: pressing the keyboard shortcut A. This might also make sense in iD, since I find myself switching between the two modes a lot.

I was considering either this or a different shortcut for each segment type, since we'll eventually have a circular type as well. I guess a single shortcut is fine since there should never be too many options.