Better search for events and spaces

[mconf-daileon]

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Author Name: Leonardo Daronco (Leonardo Daronco)
Original Redmine Issue: 1218, http://dev.mconf.org/redmine/issues/1218

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Instead of using select2 to search for events (in events/index) and spaces (in spaces/index), we could use a input that filters the results in the list of results, similarly to what is done in the list of users and spaces in the administration pages.
It seems a more complete solution than using select2 because it shows more information for the user and seems more "natural".

[daronco]

Already done for spaces in #911 and will be done for events in #917.