Change public page default view to hide insignificant by default

The public page absolutely crawls right now because there are too many insignificant events. Changing the caching policy (!150 (merged)) will help, but I am also going to propose the following:

1. Keep the wording and table structure the same
2. Hide insignificant events by default
3. Change the backend behavior so that the "show significant events only" button triggers a new database transaction, instead of loading everything at once and then hiding the html elements.

Thoughts on this, @keita.kawabe?