Create Commitment: mirror user's unit preferences from Strava

[spengrah]

If the Strava API allows, it would be nice to display the user's preferred units (e.g. miles vs. km) from Strava in our app by default.

We probably also need to allow the user to override, so we'd still want the toggle from #30

[spengrah]

Good point from @bitbeckers:

but it does interfere with the flow where a commitment could be created without a Strava login. This could be resolved by loggedIn ? noToggle : showToggle

We could also add a setting in your commitpool profile (dashboard?) to set preferred units. Maybe we can also set preferred display currency (eg DAI vs USD vs EUR) there too.