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"/>

[Sebastian Noack, 2016/07/01 15:56:04]

I wonder whether we should auto-generate the defaults based on the file
extensions actually used in the bundle using the mimetypes module.

[Vasily Kuznetsov, 2016/07/01 19:51:28]

We could, but I thought it would be more work than just using a static file.

[Sebastian Noack, 2016/07/05 14:30:37]

I don't have a strong opinion, but in the sense of DRY adding a little more
logic here would be better than maintaining a hardcoded/redundant list.
Moreover, what if future builds add files with extensions not considered here?

[Vasily Kuznetsov, 2016/07/07 16:23:48]

I implemented your suggestion and now the content type map is autogenerated. The
template became a bit shorter but more complicated, and the function that uses
it is now quite a bit longer. It might catch some extensions that were not
hardcoded before though, so at least it's more robust this way.

Done

-  <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>