CHG: some documentation and code conventions
FIX: called open again on the Shelve while clearing on an exception
CHG: added timestamp for each item in ItemStorage (tuple)
CHG: ItemStorage can now decide to optimize the amount of items (default= 1000 Items). The oldest items will be removed.
CHG: Constructor of SearchHistory only supports filename (removed plugin)
CHG: Constructor of FavoriteList only supports filename (removed plugin)
CHG: Constructor of WatchLater only supports filename (removed plugin)
CHG: Constructor of FunctionCache only supports filename (removed plugin)
CHG: Updated FunctionCache in AbstractProvider