Deprecated adUnit-level App object Methods.

[jsligh]

Deprecate the adunit-level setAppContent, getAppContent, clearAppContent, addAppContentData, removeAppContentData, clearAppContentData, addUserData, getUserData, removeUserData, clearUserData, addContextData, addExtData, updateContextData, updateExtData, removeContextData, removeExtData, clearContextData, clearExtData methods. The app object is not at the adunit level -- this design that will not work when we get to supporting multiple imps in a single auction. There are already equivalents of these functions at the global level.

Originally proposed in #977