Added a new column to the tracking parameter panel ReferencePositionEnd. Adjusted the tracking algorithms accordingly.

Added first version of the new backward tracking method. It is now possible to use interpolation methods as well.

The soundsource combination panel now shows the segment color as background if the "Update track parameter" is enabled in trajectory output.

/ Float offsets are now integrated into the table
/ Options to either use manual or calculated offset (last one not done yet)
/ Added begin and end offset for soundsources to enable input of drift (drift not implemented yet)
/ Updated GUI of track parameter

Bugfix:
  When soundsource has been applied, the zoom function was not functioning
  anymore.

Toa table:
  It is now possible to select the duplicates in the toa table, and the
  the plot will zoom to it.