Fixed parsing of requests with a URL-encoded body

~~Disabled the `mapParams` option of restify's bodyParser plugin so that the
parsed data from a URL-encoded POST body is assigned to the body property and
not params. Fixes the feedback form and any other POST endpoints that were
expecting a parsed object from a URL-encoded body.~~

Replaced all uses of the `body` field in request objects with `params` so that URL-encoded POST / PUT request bodies can be parsed correctly.

Fixes #163.

r? @cvan @yangshun @at-kevinlau