correction variable initialization
add utility functions

Function.prototype.bind method
isArray is Helper object
Add local details to challenge instances

local details correspond to a local cache for challengeInstance details
add Challenges.getInstances and update Challenge.get methods

Challenges.getInstances method request for instances and return the raw json
Challenges.get method now takes a third argument to initialize localDetails
add watchers for challenges

watchUpdates enables an event to be triggered when a challengeInstance updates.
watchAllNew enbales an event to be triggered when a new challengeInstance instance appears (invitation or yourTurn)
exposes more Challenges methods (getInstances and watcher methods)