AllPlotWindow - Alt/Slope - improve texts

... improve texts for Imperial unit setting
Google Map Overlay

.. and interval hover on marker

.. need to also show interval on hover as gray path
   but find a way of doing it without duping the code
   in the webpage js.
AllPlot: show balance in stack view only if checked
AllPlot: in Stacked View = yes / By Series = no - Curves missing

... NP, AP, XP and TE, PS curve are not shown as indicated by "Checked"

when changing between rides, "Checked" settings are ignored
Merge pull request #1089 from Joern-R/pull2

AllPlot: Some Curves missing - when "Stacked View" = "X" / "By Series" = " "
Merge pull request #1079 from Joern-R/pull1

AllPlotWindow - Alt/Slope - improve texts
Add Labels on Matches in Ride Plot

.. makes it easier to scan and see where it got to without
   having to mouse over the points one by one
Fast W'bal integration

Dave Waterworth has fixed my implementation of W'bal to
remove my "optimisations" and fix the math.

The W'bal is now computed in a single pass and is just
as fast as the differential form from Andy Froncioni but
has the benefit that is still uses Tau.

Many thanks to Dave, and I'll write this up shortly.
Auto/Stealth Ride Import when opening an Athlete

...  import Ride Files automatically from a defined Directory per
Athlete
...  runs silently/without "Import Rides" Widget if the files can be
imported/copied/... without error or warning
...  Preferences->Athlete- defines
... the directory - per Athlete and- if the function is active at all
(default is OFF)
... the error handling
... report back ALL errors and warnings by opening the RideImportWizard
popup
... report back Errors and Warnings - but ignore the "File exists"
warning (so that the import directory can be continously supplied with
new files, without the need to remove the already imported ones)
Merge pull request #1094 from Joern-R/autoimport

Auto/Stealth Ride Import when opening an Athlete
Add Running Pace Zones (1 of 3)

.. in this first part we just add the pace.zones file
   and basic configuration of critical velocity history
   in the configuration pane.

.. in part 2 we need to fixup custom zones and consider
   how they might be adjusted for VDOT/Daniels etc etc

.. in part 3 we need to add pace zones to the ridefile
   cache and then histogram and summary charts.
Copyright messages in PaceZones

.. in truth the code is largely a copy of Zones.{cpp,h}
   written by Sean, but it seemed a bit odd to not show
   that I introduced the file and the changes.

.. recognising that it doesn't /really/ matter much at all !
Merge remote-tracking branch 'upstream/master'