Improve parts of the asset map that use session storage

[smcalilly]

Some weird UX. The parts of state that are in session storage will remain when the user returns to that page and they haven't interacted in a while (if they're still using the same browser tab). The "assets successfully saved" message was still there after I had been updating a phase in the phase form and then returned to the map to add assets. The previous search was still there, too.

I think this could be fixed if we fetched the local assets via ajax after saving them, rather than reloading the entire page (which reloads the map and table with the newly saved assets.) We could then do away with session storage because the react component wouldn't reload and thus the state would remain. We would still have their search in the state and could do a more ephemeral success/error message that didn't rely on session storage.