US003: Switch activity

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User Story 003: Switch activity

As a user of the application I want to be able to switch activities so that the specified activities are stopped and a new one is started at the same moment.

Expected CLI interface:

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

yt switch New activity.
- [1] 00:15 (09:00>09:15) Currently running task's summary.
+ [2] 00:00 (09:15>) New activity.

Running activities:
[2] 00:15 (09:15>) New activity.

Activity id is provided - acting on the corresponding activity.

yt switch 1 New activity.
- [1] 00:15 (09:00>09:15) Currently running task's summary.
+ [2] 00:00 (09:15>) New activity.

Running activities:
[2] 00:15 (09:15>) New activity.

Notes:

1. When an activity is switched, it prints the id, elapsed time, start and stop timestamps for the stopped one(s), followed by its summary string. Then it also prints the id, elapsed and start time for the new activity, followed by its summary string.
2. Afterward 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-") - all those activities will get stopped.
4. A special "all" keyword is equivalent to "1-" range for activity ids.