Added new activity "Inline skating"

Decided to add a new type activity "Inline Skating", which essentialy is a subtype of existing "Skating". I observed that creating Inline Skating on one service (e.g. Garmin Connect) could result in producing an ice skating activity on other (e.g. Strava). With this change I want to fix it.
These aren't actually used for matching - so they should match the regex given in `dropbox.py`