Refactor html templates

This commit entirely refactors the use of html templates. Instead of
inheriting from a shared template, we insert the results into a base
template.

internal/dis/component/server/admin/html/users.html

@@ -1,8 +1,3 @@
-{{ template "_base.html" . }}
-{{ define "title" }}Users{{ end }}
-
-{{ define "content" }}
-
 <div class="pure-u-1">
     <div class="padding">
         <div class="overflow">
@@ -105,5 +100,3 @@
         </div>
     </div>
 </div>
-
-{{ end }}