Add route to map directly from strava

[hansonwj]

This pull request adds the functionality to allow an admin to configure rg2 to allow users to upload a recent activity directly from Strava and use them as route drawings. It makes it easier for users as they do not need to download the gpx file then reupload the file to rg2.

The configuration for admins is simple. Simply create a Strava API application and retrieve the application oAuth2 client and secret. Define STRAVA_CLIENT and STRAVA_SECRET in rg2-config.

If the oauth values are undefined, the user will not see the 'Get 10 most recent strava activities' button.

If defined, the user will see a button in the Draw tab which will allow them to sign in to strava via an oauth popup window, and the application will list their 10 most recent activities. They can then select one to add it to the map.

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I did have to bodge the existing GET listener to accept the oauth code parameter. Can't see any way around this.

[Maprunner]

This is a really nice idea but I'm afraid I am not willing to merge it into the master branch.

Strava has a set of brand guidelines that you need to comply with when using their API. This implementation does not meet any of the mandatory requirements.

Even if it did, the Strava API Agreement looks much too restrictive and would potentially require a lot of extra work that I am not willing to do.