Issue 4028 - Add support for Edge extensions to buildtools

templates/edge/[Content_Types].xml.tmpl

 <?xml version="1.0" encoding="UTF-8"?>
 <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">
-  <Default Extension="json" ContentType="application/json"/>
-  <Default Extension="html" ContentType="text/html"/>
-  <Default Extension="js" ContentType="application/x-javascript"/>
-  <Default Extension="png" ContentType="image/png"/>
-  <Default Extension="css" ContentType="text/css"/>
-  <Default Extension="gif" ContentType="image/gif"/>
-  <Default Extension="otf" ContentType="application/octet-stream"/>
-  <Default Extension="xml" ContentType="text/xml"/>
-  <Override PartName="/AppxManifest.xml" ContentType="application/vnd.ms-appx.manifest+xml"/>
-  <Override PartName="/AppxBlockMap.xml" ContentType="application/vnd.ms-appx.blockmap+xml"/>
+  {% for extension, content_type in defaults.items() -%}
+  <Default Extension="{{ extension }}" ContentType="{{ content_type }}"/>
+  {% endfor -%}
+  {% for part_name, content_type in overrides.items() -%}
+  <Override PartName="{{ part_name }}" ContentType="{{ content_type }}"/>
+  {% endfor -%}
 </Types>