Informed by user demand to support all event types rather than just talks.
Brings consistency to further align Academic and Research Group templates.
BREAKING CHANGE:
Rename `talk` folder to `event`
Remove `type` set to `talk` in any event front matter (if applicable)
To keep existing `/talk/` URLs, set the following in `config.toml`:
```
[permalinks]
events = "/talk/:slug/"
```
