Make a pp tracker per account and load on order mode boot.
Only show details on the pp tracker for the selected account.
Make the settings pane assign a `.current_pp` state on the order mode
instance (for the charted symbol) on account selection switches and no
longer keep a ref to a single pp tracker and allocator in the pane.
`SettingsPane.update_status_ui()` now expects an explicit tracker
reference as input. Still need to figure out the pnl update task logic
despite the intermittent account changes.
f16591612e