$http : ability to clear a request from the cache #5968

Previously it was not possible to remove data from $http cache (without duplicating internal functions in http to calculate the key used, which could change in the future...).

feat($http): change $http to allow removing/replacing individual requests in $http cache

Adds $http.removeCache method.
Adds/implements replaceCache property in $http request configuration.

Closes #5968