Swap "Description" and "Invitees / Details" on Calendar event views

Summary:
Ref T11326. This reorders sections:

• Description (if present)
• Recurring event series info (if recurring)
• Invitees (this also has custom stuff, if it exists)

Test Plan: Viewed some events, saw more sensible order.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11326

Differential Revision: https://secure.phabricator.com/D16671