WIP: Feature/erp5 smart backend
A backend smart enough, that can serve correctly with frontend without having knowledge about zope type.
Requirements:
- by default the non-path (
/) setup is provided/VirtualHostBase/{frontend-schema}/{frontend-hostname}:{frontend-port}/VirtualHostRoot/{frontend-path}
 - 
default-pathfromcaddy-frontendentry point has to be implemented here, as this is special case to handle the path, possibly exposed on some specific ip/port combination/VirtualHostBase/{frontend-schema}/{frontend-hostname}:{frontend-port}/{backend-path}/VirtualHostRoot/{frontend-path}
 - 
virtualhostroot-http-portandvirtualhostroot-https-portshall be extracted from request itself (trust that frontend gives proper information in the URL) 
TODOs:
- 
follow !1070 (comment 169765)