Refactor loading flag logic

[pstahmer]

The loading flags we use work with minimal dev effort, but to get there the code became harder to understand than anticipated. Additionally it is strongly dependent on naming patterns within the actions to work, which makes it a bit brittle.

Instead let's move towards a more unified store object which can hold both loading status and the data itself. Additionally if we later add a central error approach this could be folded into the model as well.