extCAD: Updated to latest upstream version

There are only two differences between this version and the upstream project:
 * config and icons: That can be set by means of create-gvsig-portable
 * JoinCADTool: The custom version of the tool can be inyected from a
   SIGA project in opencadtools, so we don't need to have it forked

As there is no need to maintain a fork create a subtree is not needed
Inyects siga custom join cad tool in opencadtools