Best aPower

Peak aPower durations now computed and cached;

* updated RideFileCache to work with aPower
* CP curve now allows you to plot aPower
* LTM plot allows you to plot aPower peaks
* DataFilter allows 'best(apower, duration)' function
Histogram aPower

Added aPower to histogram, although not zoned.
AllPlot: Add Reference Line for Power (Watts)
Read reference lines in WKO+ files

Added support for reading the 'references' or 'guide lines'
from a WKO+ ride file.
Add Derived Series to Ride Plot

You can now plot NP, xPower and aPower on the
ride plot.

This has been done to provide transparency &
insight into the relationship between the derived
values and the recorded power values,
Fix smoothing bug in Allplot for xPower and aPower
Fix crash on tmp reference line at 0w
User definable color for W' bal curve
UI Nits: Center Preferences/Options pane
Find Matches

Added auto finding matches in Wprime, but there are
two areas to develop further;

1. Use the W'bal data to find matches instead of the
   power above CP (which is really being used as a proxy
   for the better approach).

2. Update the 'find intervals' dialog to allow you to
   find matches and add them as normal intervals.

Pushing to repo as a version checkpoint, this function
will definitely need refining before 3.1 is released.
UI Nits: Axis background color

Changed to match the ride plot background. This makes
it easer to read axis that use light colours (e.g.
using yellow for power).
Find Matches as Intervals

Now let the user add 'match' intervals in
the find intervals dialog by setting a minimum
cost for the match.
Match duration fencepost error.
Zoom Out Menu Option

So you can unzoom in ride plot when you've zoomed in
to an interval -- avoiding having to show fullplot to
do the same thing manually.

There are probably other places to add functionality
for zooming out, will deal with those as they arise.
UI Nits: Declutter ride plot

Too much going on and gets noisy, especially in stack mode.

Might extend this to the other plots, but need to live with
it for a while to see if the ticks were actually useful (!)
UI Nits: Less is more

Further removal of chart decorations ala the recent
changes to the ride plot, now applied to the other
charts.
UI Nits: Thinner reference line

2px too thick for a guide, made 1px which is in
line with the rest of the code.
UI Nits: Less Ride Plot xBottom

.. no title needed for time, its obvious, but
   still need to show units if its distance.
UI Nits: Back to black in QA

.. the washed out grey was unpopular and is too
   hard to read.
UI Nits: Matches markers lower

.. so they don't clash with other interval markers
   most especially user supplied interval marks