Add old_calls cli command

[bundasmanu]

In multiple cases, its useful to have a cli command that show calls older than a specific time threshold.

At this time, we don't have a easy way to do that.
We can do the query directly to DB or parse the show calls|channels output.
But its boring, and hard to mantain in monitoring tools.

---

Added a new cli command:

• show old_calls <time_threshold_seconds> [as] [json|xml|...]
  • time_threshold_seconds its optional - must be defined in seconds;
    • Example: 1 hour --> 360 seconds;
    • By default , the threshold is 1440 seconds (4 hours);

---

Tests:

Oh, yes.

• Without passing time threshold;
• Passing custom time threshold;
• Return as json|xml;