Adds a new item into the user context store.
Id
A System.String that identifies the item to be stored.
data
The an array of System.Byte to be inserted as the item information.
priority
The precedence of the stored item relative to other items stored, check the System.Web.Caching.CacheItemPriority enumeration.
dependency
A path to a file that is related to the inserted item, when this item is deleted this dependency file will also be deleted.