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.

Conflicts:
	src/DBAccess.cpp
	src/WPrime.cpp