extractorapp - add metadata extraction in client-side extractorapp

* only works for layers listed WMS 1.3.0 GetCapabilities
 ie. no support for WMS 1.1.0, WFS, nor WCS
* created a branch of template config to test with some layers
  * reg22:lycees_adresses - extraction of metadata (ISO19115:2003 type and text/xml format)
  * sernap:APs_regionales - extraction of metadata (ISO19115:2003 type and text/xml format)
  * sernap:APs_municipales - no extraction (FGDC type and text/plain format)
  * reg22:Pays_2013_BYcplet_FLA10 - no extraction (no metadata in GetCapabilities)