Refactory Buefy templates to use WholePage and ThisPage components

plus add `GridFilter.set_choices()` method

tailbone/templates/login.mako

@@ -1,5 +1,5 @@
 ## -*- coding: utf-8; -*-
-<%inherit file="/base.mako" />
+<%inherit file="/page.mako" />
 <%namespace name="base_meta" file="/base_meta.mako" />
 
 <%def name="title()">Login</%def>
@@ -24,12 +24,17 @@
   </div>
 </%def>
 
-${self.logo()}
+<%def name="page_content()">
+  ${self.logo()}
 
-${self.login_form()}
+  ${self.login_form()}
 
-% if request.rattail_config.demo():
-    <p class="tips">
-      Login with <strong>chuck / admin</strong> for full demo access
-    </p>
-% endif
+  % if request.rattail_config.demo():
+      <p class="tips">
+        Login with <strong>chuck / admin</strong> for full demo access
+      </p>
+  % endif
+</%def>
+
+
+${parent.body()}