converse-register: refactor in order to simplify.

src/templates/form_url.html

+<label>
+    {{{label}}}
+    <a class="form-url" target="_blank" rel="noopener" href="{{{value}}}">{{{value}}}</a>
+</label>

src/templates/registration_form.html

 <legend>{{{__("Account Registration:")}}} {{{domain}}}</legend>
+<span class="reg-feedback"></span>
 <p class="title">{{{title}}}</p>
 <p class="instructions">{{{instructions}}}</p>

src/templates/registration_request.html

 <span class="spinner login-submit"></span>
-<p class="info">{{{info_message}}}</p>
+<p class="info">{{{__("Hold tight, we're fetching the registration form…")}}}</p>
 {[ if (cancel) { ]}
-	<button class="pure-button button-cancel hor_centered">{{{cancel}}}</button>
+	<button class="pure-button button-cancel hor_centered">{{{__('Cancel')}}}</button>
 {[ } ]}