Add pagination and server-side filtering to events list on main page

[lpsinger]

The main events list page takes a long time to load because it reads and displays all events in the database. We can speed it up and make it more responsive by doing pagination and filtering of the result set on the server side like we do for the galaxy catalog view. We might even want to generalize the DataTables interface from the galaxy catalog so that we can reuse some of that code for the event list.