Save Stopwatch activity context in Journal

[llaske]

The Stopwatch activity don't use Journal to store the activity context.
It could be nice to store values for current counters and intermediate times in the Journal so when the activity is reopened, all values will be retrieve.

[llaske]

Code of Stopwatch activity is located here https://github.com/llaske/sugarizer/tree/dev/activities/Stopwatch.activity
To handle datastore in an activity, see tutorial here: https://github.com/llaske/sugarizer/blob/dev/docs/tutorial_step4.md

[llaske]

Fixed in #228