Issue with tabs on the track properties window

[davidedelvento]

The tabs seem to be in semi-random order, namely:

Elevation-distance
Gradient-distance
Speed-time
Distance-time
Elevation-time
Speed-distance

A more sensible order to me seems:

Distance-time
Speed-time
Speed-distance
Elevation-time
Elevation-distance
Gradient-distance

or

Distance-time
Speed-time
Elevation-time
Speed-distance
Elevation-distance
Gradient-distance

I can send PR if you think this reordering is appropriate and which one you prefer (if any)

[davidedelvento]

Created PR #34 - let me close this and have any discussion there if necessary