Calendar Chart now honours colour preferences

.. think that is the last of all the charts now done.
No smoothing applied when smooth < recIntSecs

.. its pointless

.. it is a big performance overhead

Fixes #753.
Turn smoothing OFF if smooth < recIntSecs

.. i.e. don't do ANY smoothing

.. last commit fixed performance but really adds
   no value to smooth data to the interval it was
   recorded at !!
Don't allow 0 smoothing in compare mode

.. we need all intervals to have a common smoothing
   applied or it breaks the charts
Merge pull request #903 from Joern-R/pull1

Translation Enablement & consider "seconds" translation
Fix time tooltip on AllPlot
Fix useMetric in Scatter plot

.. was broken when we moved useMetricUnits to the
   Athlete class and a local bool remained.
Fix color or red wavy line text

.. in the ride editor
Fix new CP chart show bests

.. didn't show bests and model till date range changed
   in settings or GC was restarted.
Darker flat chrome Linux/Win

.. makes for a better match to the chartbar and sidebar
   items when in flat mode and not on a Mac.
Fix Overlay Widget colors

.. and along the way discuovered context is not initialised
   correctly in GcChartWindow !
Translation Enablement & "seconds"

... more tr() changes
... added comparison for  both "seconds" OR tr("seconds") to all other
occurences found
... added "Lap" text for Intervalls imported in Garmin FIT format (this
is what Garmin delivers)

(cherry picked from commit ad790f05a386e3ae5c5b9dc129a216ac451b8cfc)