API class, SOM class(es), Rides class, LatestMapWidget

Hey Carlos,

I reworked all the HTTP requests to use the WordPress API via the WPStrava_API class.  I also created some SOM classes to abstract that functionality out so we can use it for all shortcodes/widgets.  This shortened up the Rides class a bit, but I added some more methods to it.  I also added a WPStrava_LatestMapWidget that I wanted to complete.

I haven't (yet) incorporated all of these changes into the shortcode, but I wanted you to look at the progress to see if you like the direction.

Also, these guys have fairly simple plugins:

http://wordpress.org/extend/plugins/simply-strava/
http://wordpress.org/extend/plugins/strava-ride-details/

We could potentially bring them in as collaborators to create the canonical go-to strava plugin.  Let me know what you think.