Filter out deleted events #44

`deleted=true` param in URL displays deleted events in addition to not deleted ones.

`deleted` parameter is exposed in JSON API.

Direct request to a deleted event is not blocked in any way.
Style/HashSyntax: Use the new Ruby 1.9 hash syntax.<br>Style/SpaceAfterColon: Space missing after colon.<br>Style/SpaceAroundOperators: Surrounding space missing for operator '=>'.<br>Style/SpaceInsideHashLiteralBraces: Space inside { missing.<br>Style/SpaceInsideHashLiteralBraces: Space inside } missing.<br>Style/SpaceInsideParens: Space inside parentheses detected.