Site-specific error pages

Site-specific error pages (see description in the DOCU-58) are not working now as there are notsite-specific folders anymore.

We need to specify a correct place (/jsp/jahia/errors/<site-key>/ ?) and adjust the implementation.

The sequence can be as follows:

• look into a site-specific folder, e.g. /jsp/jahia/errors/<site-key>/
• look into template set specific folder, e.g. /jsp/jahia/templates/core_templates/errors/ (should we consider inheritance here, i.e. to lookup in the parent template sets also?)
• use default error pages from /jsp/jahia/errors/ folder

Please validate this and add your notes, suggestions and so on.

Thank you!