Replaced reqparse with a custom parser

The parser's code has been copied from Critiquebrainz.

A new method for 'anything' type has been added along with some other
miscellaneous changes.
Updated the create user API endpoint

Now uses the custom parser.

A 409 Error is raised if the user already exists.

201 Code is returned if the user is created, rather than 200.
[hack] Login the user after creation

This is BAD as the API should never be used to login a user, and is only
temporary.

Once we have a better registeration process (one invoving email id
verification) this can be changed.

The other fix might be to remove ajax and use a form similar to the
login page, but that means the create_user code gets duplicated.
Registeration form complete

Ajax call to /api/1/users/

Currently an alert message is set; in future, we can use popovers over
input boxes.