Add "build" tools to the mgmt image
Add "build" tools to the mgmt image

* composer for PHP
* node and npm for JS
* gnupg because Node's install script requires it to check the
  integrity chain

Neither requires a runtime, therefore there is no need to make the
same change to the httpd image.

epfl-idevelop/jahia2wp,epfl-idevelop/jahia2wp,epfl-idevelop/jahia2wp,epfl-idevelop/jahia2wp