Implement function / datas structure to conveniently aggregate all
query-related data, for reuse in various places in mu4e...
... to start with the main menu, which gets much simpler. And the
modeline.
Usurp more of the utils code than can be re-used without further dependencies in
helpers.
Split off specific parts in their own file.
After the helper/utils changes, update the rest of mu4e to take the changes into
account.
