Add missing fields on the `Meeting` model

I was prompted to review the Meeting model by the question asked by @SilverrainSPB in #289 and I noticed a few fields that were added to the Zoom model over the years but our model has not been updated accordingly.

More specifically, the following fields are missing from the model in ZoomNet:

[x] assistant_id
[x] host_email
[x] encrypted_password
[x] pmi
[x] pre_scheduled
[x] tracking_fields

I also notice that our model includes a field for pstn_password but this field is not in the documentation. For a moment I considered removing the field but I found a post on Zoom's devforum where a Zoom employee defines what this field is which leads me to conclude that this is a legitimate field and that it should remain in our model despite the fact that it is not documented.

Jericho / ZoomNet

Add missing fields on the `Meeting` model #290