A separate filter page lets users search more precisely for events or organisations, in different formats

Event calendar better displayed on small screens: past events only visible when hovering over the current month

as recommended in RFC 3986 section C (ftp://ftp.rfc-editor.org/in-notes/rfc3986.txt)

Close #77

The parameter that can be used to have future *and* past events in the rss feed is renamed to `future`

RSS feeds can be easily parsed and hence can be used to populate program for
events with the proper tags. By adding the 'showall=true' to the query string,
it is possible to see all events corresponding to the requested criteria in
the RSS feed, whether past or future and more than 20.

Signed-off-by: Geneviève Bastien <gbastien@versatic.net>