BaseBasket: Make `load` method private
BaseBasket: Make `load` method private

Rename BaseBasket's `load` method to `_load`, because it exposes the
internal structure of the basket which should not be public to allow
easier refactoring.

Refs SHOOP-975

taedori81/shoop,hrayr-artunyan/shuup,jorge-marques/shoop,suutari/shoop,shawnadelic/shuup,suutari/shoop,taedori81/shoop,shoopio/shoop,akx/shoop,jorge-marques/shoop,taedori81/shoop,hrayr-artunyan/shuup,suutari-ai/shoop,shoopio/shoop,suutari-ai/shoop,shawnadelic/shuup,akx/shoop,hrayr-artunyan/shuup,shawnadelic/shuup,suutari/shoop,jorge-marques/shoop,shoopio/shoop,akx/shoop,suutari-ai/shoop