Move `budgeteer-rest` method security expressions into a separate module and replace the `budgeteer-web-interface` ones

[czarnecki]

Both budgeteer-rest, and budgeteer-web-interface use method security expressions. Both modules use their own implementations which mostly do the same things in different ways.
As part of the ongoing effort to unifiy the old and new backend we want to use the new implementation from budgeteer-rest for the budgeteer-web-interface. And to properly allow for that we should move that into it's own module, and replace the budgeteer-web-interface implementation.