handle relations in show mode

fix #306

porting the configuration for show templates from the orm admin.
all 4 twig files are exact copies of the orm templating. this makes me wonder why we do not push them up into base admin. everything doctrine specific is in the twig extension and elsewhere (as it should be). @pulzarraider wdyt?

we still need to add them here i guess, to not now bump the version requirement on the base admin.