Merge branch 'freediving-tweaks' of git://github.com/mguentner/subsurface

Merge freediving tweaks (zoom in on short dives etc) from Maximilian
Güntner.

Trivial conflicts in display.h due to unrelated printing stuff just
happening to be added nearby.

* 'freediving-tweaks' of git://github.com/mguentner/subsurface:
  moved zoomed_plot to display.h
  plot the time with a fixed padding (leading zero)
  updated/corrected comment
  added "Zoom" button and improved scaling
  fixed indentation
  use increments that make sense for 600 seconds
  Plot shorter (apnea) dives with a reasonable scale