better explanation for what happens when track marked as secfondary.  Fixes #770
Fixes 768
improve text, fixes #766
fixes #765
fix formatting
Fixes #761
Fixes #760
fix for loading DR track
Merge pull request #775 from debrief/issue759_FitToWindow

fix for loading DR track
Fixes #754
Fixes #750
Fixes #747
handle instance where old value of editable is null
clear initial frequency values, so the popup menu stays empty
Fixes #745
Merge pull request #774 from debrief/feature/ian/more_cheat_sheet

Cheat sheet updates
Merge branch 'master' into issue575_freq