Merge pull request #547 from amtriathlon/master

Enabled translation of supported devices legend in DeviceTypes.cpp
Fix stresscalculator 2-a-day bug.

If >1 rides per day stresscalculator ignores after the first
ride, this was caused by a flawed strategy for seeding the STS
and LTS with non-zero values.

We now seed with negative values and switch signs as we pass over
the date during calculation.

Fixes #549.
Enabled ScatterPlot axis legend translation
Merge branch 'master' of https://github.com/GoldenCheetah/GoldenCheetah