More complex modes of track manipulation

[KaiMartin]

Please add some more complex modes of track manipulation:

 a) Insert an elbow: "______" --> "___/\___"

 b) Insert a plateau : "______" --> "_/---\_"

 c) Push tracks out of the way, while drawing other
    tracks. (Like protel99 does)

 d) Vias should be placed, if a track gets flipped to
    the other side with the m-key.

 e) Automagically reduce the size of a track if this is the only way to wiggle into some tight space. Return to the original track size when space allows.

These would make manual routing easier, if board real estate is at premium.
---<(kaimartin)>---