Search enhancements: recursive search; search on event attributes

[duncanka]

Added two features to search:

1. When searching a collection, it is now possible to select a "recursive" option in the advanced options to enable searching subdirectories.
2. Event search now includes options for searching for particular attributes. Blank or unchecked attributes are ignored; checked boolean attributes and string-valued attributes are used as filtering criteria in the search.
   Only attributes relevant to the selected event type are selectable. For hierarchy-only event types and the default selection of "- Any -", attributes relevant to any of the subtypes are available. The same rule has also been applied for the existing role search functionality (e.g., all roles are available if '- Any -' is selected).