Configure SearchEngines at init-time, not on first use
Don’t reindex Events and Venues when configuring Sunspot

This takes a rather long time with a large database and shouldn’t happen
every time the app is started.
Reindex models after switching to Sunspot in specs
refactor tag cloud to use acts_as_taggable_on's tag cloud codepaths.
extract Event::Overview.
narrow interface between controller and view.
move Event.select_for_overview to Event::Overview.
expose hash keys as methods.
extract some private methods.
move event separation into methods.
tweak tests.
refactor event overview tests.
test ApplicationHelper#tag_links_for
test ApplicationHelper#datestamp.
test and refactor EventsHelper#tweet_text.
test EventsHelper#today_tomorrow_or_weekday.
refactor MappingHelper.
remove untested and unused relative option in TimeRange.
test SourcesHelper.
Remove uncalled Event#to_hcal and associated test