Issue #11 fix availability slider, submits values, ignores negativ hours
slide control values <0 are a problem still
don't try to access deleted objects (delete message)
Removed current Conference from the dropdown for "Switch Conference". #17
Added optionally schedule version into public schedule and public export.
Issue #27.
fix recent changes problem with deleted things
Fixed another recent changes user id not found bug.
Disabled public schedule for non admin user.
Integration of a JSON Api using erb-template
This commit implements a small JSON API which tries to serve the same
informations as the XML API. It is needed hardly by mobile app developers
which previously build their own "proxies" for lightweight JSON using
PHP and had to switch its url for every event they wanted to build an
app for.

There are several reasons to avoid this:

* This adds one more point of failure to external thrid party apps.
* It causes every third party developer to build his/her own proxy.
* After all, every developer has to host the proxy on his own server.
offer JSON Api to users
Add id to title on event cards.

As requested in #18
Add (very) basic tests for public schedule.
Remove superfluous statements.

Rails' defaults are exactly the same here, so we can get
rid of this and make the controlly a tiny bit leaner.
Added another graph into call for paper show view. It shows the sum
of submissions compared to the time.
Enabled public schedule without authentication again.
Fixed static export script.

Used Marios changes in the static program export script to fix the
encoding and modification errors while the export. Additional to the
export fix, new scopes were added to person (get all people with a
confirmed event) and event (get all confirmed events) model.
Bloody workaround for room names in pdf schedule export,

The header cell in the exported pdf schedule table is not prepared
for room names greater than ten characters. This hot fix cuts every
string after one word character, at least 2 digits and a slash as
identifier.

Examples:
  C118/Java (Sa), Python (So)
  => C118

  HS1/2
  => HS1/2
Added room in schedule event view.
Fix off-by-one in max timeslot selection
Fix users not being deleted with persons and display of versions for deleted users