Switch UI logic to use a temp-store

Probem

When editing some Rule elements, the Rule is active and executed. E.g. if you remove a condition to add another one later, the moment the first condition is removed, the rule is active and might be executed wrong in the background.

Proposed solution

Move to a temp-store / object store approach as Views does. The object store got moved to core for views, thus is available for us to use. It would hold all the currently edited configurations and get all the changes of the user. Thus the UI loads and writes always to the temp object store, until the user presses the save or cancel button finally.
We'll need to show a yellow warning on top of the UI that changes need saving just as Views does also.