Events Upgrade Path

In this pull request:
re: https://devspace.stanford.edu/jira/browse/DRPL-412

* Cleaned up hook_schema and db installation + upgrade checks for latest schema
* added hook_update_7201
  * Reverts all components of the feature
  * Invalidates hash key for each imported item
  * Updates the importer feed URL for each importer
  * Changed default input format to Y-m-d g:i:sA for field eventdate
  * Makes sandwiches :)
* Updated documentation to reflect the new upgrade path features