Work Offline

## Problem

Several actions in the Tasks app requires the user to have internet connection. Right now it is not clear which actions do need network and which don't. This situation leads to a bad user experience.

This issue is here to track the needed changes.

## Proposal

- [ ] Add offline support and sync changes as soon as internet connection is available
- [ ] Wherever this is not possible, enable/disable user facing actions depending on current network status

The best thing to do is to add full offline support with syncing changes whenever network connection is available. However, at the time of writing, it is not clear if this is possible for all actions. Wherever this is not possible, we should enable/disable the action depending on the network connection and clearly communicate why an action was disabled (using a hint message or similar).