New Metrics for MTB - Bike Carrying Time/Elevation Gain

... 2 new metrics (estimates) mainly relevant for MTB or Race bike steep
passes
... a) Time Carrying = moving < 8kph, gaining height, no power, no
cadence
... b) Elevation Gain carring = same criteria, but adding up the
elevation gain

Since there is a certain level of error, the metrics is named as "Est".
Merge pull request #1050 from Joern-R/pull3

New Metrics for MTB(mainly) - Bike - Time Carrying / Elevation Gain Carrying