Correct reference to 'firstname' when populating forenames from Strava.

See: http://strava.github.io/api/v3/athlete/

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>
Also populate Strava name from 'lastname' attribute:

Ref: http://strava.github.io/api/v3/athlete/

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>
Merge pull request #336 from lamby/strava-name-populate

Strava name population fixes