Merge pull request #67 from Ptizef/master

 Take file's time steps when "interpolate" option is uncheked and improve timeline scrolling
Merge pull request #68 from Ptizef/master

Improve grib data panel ( Add unit symbols and use all available space for data )
Correct SENC Text formatting
Optimize layer trackpoint listing logic in RouteManagerDialog
Improve performance of track rendering at small scale.
Improve NavObjChanges logic to prevent infinite looping