Fix Bug 897756 - Event dates should be in separate field

Original Commit by @hdanak: https://github.com/AmoebaConsulting/webmaker-events/commit/7745b55cf67abe8bfd489b1df9681f92574ab320
Fix Bug 897758 - Add attendee estimate to admin page

Original Commit by @hdnak : https://github.com/AmoebaConsulting/webmaker-events/commit/be9f362da2cee9203c84a9891b916037529f7547