Close the request body with a middleware instead of within the handler function body

[tiagoalvesdulce]

As mentioned by Luke here: #84 (comment).

We already have the middleware defined here:

dcrtime/dcrtimed/dcrtimed.go

Line 1297 in bbebe6d

func closeBody(f http.HandlerFunc) http.HandlerFunc {

And are using it here:

dcrtime/dcrtimed/dcrtimed.go

Line 1306 in bbebe6d

func (d *DcrtimeStore) addRoute(method string, route string, handler http.HandlerFunc) {

As we add every route with the addRoute method. It should be already working so the calls to defer r.Body.Close inside handler functions are redundant and can be removed.