Make new events top level by default

[absempere]

New events and projects should be at the top level (not subpages / nested) by default.

The main reason is that on the home page, there was too much repetition of content, and when we suppressed the "home" link, all of the tables of contents started to look wonky. So everything should be top-level, and users can add structure if/when they'd like.

We should make sure to check that the home page and the side navigation on published sites both look correct.