- fix restoredIncompleteOrder: this needed a single-shot return; observer-based cycled
infinitely through restorable orders as each was "reset" to clear saleItemIds and set
current date. Solved with new incompleteOrderFuture method
- fix KDSOrderView did not update with additional saleItemIds added after initial item:
solved removing `.removeDuplicates()` operator
- fix saleItemIds not clearing for X-Cancel-order button action: solved by tombstoning
saleItemIds MAP (rather than tombstoning all individual key/vals). Subsequent additions
recreates the map and adds values implicitly
- fix add "WHERE id" clause on resetQuery, clearSaleItemIdsQuery  which, when failing were
no-ops but would have cleared all saleItemIds in all orders

This feature allows user to switch between hard-coded restaurant demo locations
and creating their own custom user-defined location. An Advanced Settings detail
view added to Settings view enables switching between the two modes at runtime.

- add Settings abstraction as interface to UserDefaults for persistent read/write
app state variables; some DittoService-centric moved to Settings
- add handling for detecting various location setup states at launch
- add handling for presenting/dismissing views relating to switching modes
- add AdvancedSettings detail view to SettingsView with locations mode toggle