Add initial work for differential synchronisation
Handle deleted tasks in syncedDevice
Add persistance for syncedDevices
Add interface component to handle paired devices
merging from master ; integrating deleted tasks for sync
devices are identified and can now be saved
devices saved in wifi
Minor refactoring of SyncedDevice

- Add the date in the constructor instead of as a parameter
- Remove a useless constructor
- Remove a deprecated methode (toLocaleString)
Don't change fragment twice when exiting EditTaskFragment

May solve #14
[TaskListAdapter] also notify projects adapter when notified
Update the project list when changing the project of a task
Add method to get the timestamp of the oldest updated peer
Added differential sync : devices are saved when syncin, and a
differential task list is built before sending data if the other device
is already known
Rename the application and the package
Notify the adapter when we remove a synced peer

may solve #16.
update peer list instead of just adding a peer, there are no more duplicates
fixed peer list, now correctly prints a peer with the date of last sync
fixed unchecked operations when deserializing peer list