Use pre calculated values from .fit files

[seanmorley15]

Currently the app ignores valuable pre-calculated metrics for distance and elevation that FIT files from Garmin and other devices typically contain. It appears as though this data is recalculated as a GPX file leading to some inconsistencies. For example Garmin Connect might say 5.5 miles but the recalculated value is 5.8. Using the pre calculated values FIT files have will keep it consistent across platforms.

I took a look at the code and plan to work on this myself once I have time :)

Thanks!