Reorganises internal state

`options` slice was huge and managed a mix of generation parameters and general app settings. It has been split up:

- Generation parameters are now in `generationSlice`.
- Postprocessing parameters are now in `postprocessingSlice`
- UI related things are now in `uiSlice`

There is probably more to be done, like `gallerySlice` perhaps should only manage internal gallery state, and not if the gallery is displayed.

Full-slice selectors have been made for each slice.

Other organisational tweaks.

invokeai/frontend/src/features/system/components/ModelManager/SearchModels.tsx

@@ -17,7 +17,7 @@ import {
   setFoundModels,
   setSearchFolder,
 } from 'features/system/store/systemSlice';
-import { setShouldShowExistingModelsInSearch } from 'features/options/store/optionsSlice';
+import { setShouldShowExistingModelsInSearch } from 'features/ui/store/uiSlice';
 
 import _ from 'lodash';
 
@@ -128,7 +128,7 @@ export default function SearchModels() {
   const existingModels = useAppSelector(existingModelsSelector);
 
   const shouldShowExistingModelsInSearch = useAppSelector(
-    (state: RootState) => state.options.shouldShowExistingModelsInSearch
+    (state: RootState) => state.ui.shouldShowExistingModelsInSearch
   );
 
   const isProcessing = useAppSelector(