Derive Slope Data

- If Alt data present then calculate slope
- Smooth the slope data after calculation
Add Fenix2 to Garmin Devices
Revert "Add Fenix2 to Garmin Devices"

This reverts commit c6112bd13ca4d1d3a407ebe75bc2bff7afd5ca8b.
Add power estimation

Need to be able to add parameters for users to adjust their drag factors
numbers currently work out not too bad for me but needs testing with
more ride files. I have tried it with Mark's Marmotte file and it
doesn't do too bad.

Please feel free to rip it apart and tell me it is wrong - its a good
start hopefully.
Merge pull request #995 from jonbev/upstream

Add Derived Data (slope & power so far)