Add convenience wrapper to make customer field widget, etc.

customer widget is either autocomplete or dropdown, per config

also added a way to pass arbitrary kwargs to the chameleon template
rendering for a field

also moved the logic for rendering a <b-field> out of the template and
into the Form class

also start to prefer `input_handler` over `input_callback` when
specifying client-side JS hook

tailbone/templates/forms/deform_buefy.mako

@@ -1,5 +1,4 @@
 ## -*- coding: utf-8; -*-
-<%namespace file="/forms/util.mako" import="render_buefy_field" />
 
 <script type="text/x-template" id="${form.component}-template">
 
@@ -21,7 +20,7 @@
             </b-field>
 
         % elif field in dform:
-            ${render_buefy_field(dform[field])}
+            ${form.render_buefy_field(field)}
         % endif
 
     % endfor