Fix Bug 897756 - Event dates should be in separate field

Original Commit by @hdanak: https://github.com/AmoebaConsulting/webmaker-events/commit/7745b55cf67abe8bfd489b1df9681f92574ab320
Merge branch 'bug897756' of https://github.com/cadecairos/webmaker.org into bug897748
Made beginDate and endDate required fields; still no feedback in UI