US002: Stop activity

[ototo]

User Story 002: Stop activity

As a user of the application I want to be able to stop any of the currently active activities.

Expected CLI interface:

No activity id provided - acting on the most recently updated activity.

yt stop
- [1] 00:15 (09:00>09:15) Currently running task's summary.

Running activities:
[2] 00:10 (09:05>) Another running task's summary.

Activity id is provided - acting on the corresponding activity.

yt stop 1
- [1] 00:15 (09:00>09:15) Currently running task's summary.

Running activities:
[2] 00:10 (09:05>) Another running task's summary.

Notes:

1. When an activity is stopped, it prints the id, elapsed time, start and stop timestamps for it, followed by its summary string.
2. Afterwards it prints the list of running activities with their respective ids, elapsed times, start timestamps and summary strings.
3. It is also possible to specify a list/range of activity ids (e.g. "1-3,5,9-").
4. A special "all" keyword is equivalent to "1-" range for activity ids.