TODO before 0.12.0 release:

* ~~Support importing Pebble Health data from old database~~ DONE, needs check.
* ~~Add onboarding activity on first startup (to merge old data)~~ DONE, needs check.
* export db/delete db improvements
* ~~onboarding hint about import-db in Debug activity~~ DONE, needs check.
* TESTING!
* tx pull

Non blocking issues:

* Add back UUID_CHARACTERISTIC_PAIR support, at least optionally
* CSV Export