Website updates
Run: lupdate-qt4 src/src.pro

Update the translation source files
Add NP and xPower Derived Data Series

Calculate NP and xPower as a data series so we can
plot on the ride plot.

Have also added 'aPower' which will be coming in the
next few days - altitude adjusted power, which will also
have some associated metrics (a-xPower, a-NP, a-TSS etc).
Add aPower

Introduce altitude adjusted power 'aPower'.

This is a new ride data series that takes into account
the effect of altitude on power output.

At present we are only adding this as a derived data series
with the intention of making it possible to plot it on
the ride chart.

We will also introduce alternate metrics for average power,
bikescore etc that are based upon the aPower value.
Average aPower

Added an average aPower metric.

I also and found and fixed a couple of bugs along the way;

* intervals create a ridefile and need to explicitly call
  recalculateDerivedMetrics()

* the aPower calculation was using the calculated vo2max
  percentage the wrong way around (!)
Add citation and references for aPower

Added comment in ridefile.cpp to reference the book
and research paper that aPower is based upon:

// Calculate derived data series, including a new metric aPower
// aPower is based upon the models and research presented in
// "Altitude training and Athletic Performance" by Randall L. Wilber
// and Peronnet et al. (1991): Peronnet, F., G. Thibault, and D.L. Cousineau 1991.
// "A theoretical analisys of the effect of altitude on running
// performance." Journal of Applied Physiology 70:399-404
Added Effect of Altitude (%)

A metric of the %age of power that has been lost due
to riding at altitude.
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.