Add timeline

[KTibow]

Is your feature request related to a problem? Please describe.
When you open SimpliSafe's app or webpage, you can click to see a timeline with past events.

Describe the solution you'd like
I'd like a way to do something like get_events() and get past timeline activities.

Additional context

• I'm not sure if there's a difference between events and the timeline, but I'm pretty sure they're different because events get cleared and the timeline doesn't.
• Later on, it might be useful to download associated videos.

[bachya]

system.get_events() utilizes the same underlying API as SimpliSafe's Timeline view. You can retrieve past events by altering the from_timestamp parameter: https://simplisafe-python.readthedocs.io/en/latest/system.html#events

Downloading associated videos will likely be a part of what solves #85.