R1:684805a88a16

Move rendering to SearchEngine for Calendar

Summary:
Ref T4986. This one needs `getApplicationURI()` so make it a little beefier to deal with that.

(It would be vaguely nice to somehow share the handle and application stuff between Controllers and Engine classes like this, but I don't immediately see a clean way to do it without traits. Not a big deal, in any case.)

Test Plan:
- Viewed Calendar.
- Made a Calendar panel.
- Viewed feed.

Reviewers: btrahan

Reviewed By: btrahan

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