Allow display error on ... error & prevent token url error & Add link to thelia modules

This PR is a gift to @roadster31 , solving his #935 .
Now, thelia has error pages too. :kiss:

This PR solves #939 too.
This solves #938 too.

Explain how ti use this fallback please. This feature is disabled by default so if you don't explain how to use it, nobody will use it.

Thanks