Track editing will be the most powerful yet most difficult to design/implement feature in Viking

Basic Requirements:
1) Dragging trackpoints by mouse
2) Examining & Setting exact lat/lon (and time)

Things we need to be able to do:
* Join and separate Tracks, and segments of tracks.
* Delete segments of tracks
* Delete individual segments, preferably both leaving a gap and directly jump to the next point.
* Add on to tracks, on end, middle, or insert trackpoint, with option 'new segment' flag.
* Select track segments to copy & create a new track
* Move/pan whole tracks
* Maybe by hovering over a trackpoint, displays diff in time and space (displacement AND distance 
  along track) from selected trackpoint

With these things, we can accommodate most common procedures. For example: user wants to change 
one part of a track by going a different route, but rest of track is OK. User:

1) Loads old track and new data.
2) selects part of old track that is no longer valid, deletes that segment.
3) Clips of any excess data or adds any trackpoints that are needed to join tracks.
4) joins two track segments and new track data together to form one track.