Add user preference for filtering of GPX speed data

[jat255]

This PR partially addresses #48 (although it's not perfect).

Basically, it adds a new user preference (use_raw_gpx_speed) that instructs FitTrackee to pass raw=True to gpxpy's get_moving_data method when parsing a GPX file. It works as advertised, but it's not really a perfect solution. Perhaps a better/more flexible solution would be to add a preference that gets passed to that method's speed_extreemes_percentiles parameter, which would allow for tuning of the behavior (including setting it to 0, which would be the same as raw=True). I could do it that way if it's better.

Ultimately, this seems (to me) a limitation of how gpxpy implements filtering, which is to calculate all the speeds for the GPX file as-is and then discard some percentage of the top ones. Other GPS applications appear to eliminate actual GPS outlier points (see this part of GPXSee for example)

I added translations for the new user preference strings, but they're just from google translate, so they could probably use some review.

Here's what the preference setting looks like:

[SamR1]

Hi,

thanks for the PR.