run queries in parallel
decrease timeout
do not fall back to google

* introduce notification channels
* always use foreground service on 26+

Merge branch 'start_convervsations_by_long_press' of https://github.com/ChaosKid42/Conversations into ChaosKid42-start_convervsations_by_long_press

Based of initial worked by @harshitbansal05

This makes sure even misconfigured PEP nodes still get only one item, as
defined in XEP-0060 §12.20.