Fix a minor bug in the playground app, resulting in 404's in some cases.

For some reason, the browser keeps appending a trailing '/' at the end
of the URLs. Since the loadExample function in playground.js parses the
request parameter itself and uses it to load the JSON, a trailing '/' at
the end of the URL causes the function to generate a request for a JSON
named '.json'.

The PR adds a check for a trailing '/' and taking appropriate action if
there is a trailing slash.
Merge remote-tracking branch 'abhinav-upadhyay_jsonform/fix-playground'
Upgrade to Bootstrap 3

Upgraded to support Bootstrap 3. Might not be comprehensive, and drops
support for Bootstrap 2.
Handle more than one type.

If jsonform encounters a form element with more than one type, first
tries to remove null and set as not required, then throws an error if
there's still more than one type. Compatible with Json.NET Schema
Generator.