added check on already added coach
added a stateless way of specifying whose data the user currently chooses to look at (either his or one of his coachees')
thanks to the new stateless viewee selection mechanism, we don't need to reload the entire page anymore.

Choosing the user's who's data the user wants to look at results in setting a globally accessible variable (App.viewee). This is then used to specify the X-FLX-COACHEE-USERNAME header when user data ajax calls are sent to the server.
undefined check
undefined check
added the coachee username header everywhere it's needed
coach also needs to be added to the AuthHelpers current list of viewers
updated the shared connectors endpoint to return a proper model class (easier for documentation) and use a better URI
not promise json if we're not generating any