exchange "kotti" by "external" (see #836)
allow instance-sepcific staticpages api address
link to staticpages inside instance

if instance specific staticpages are enabled.
Affects only external navigation and entity_url.
help_link inside instance if instance-specific staticpages
fix remaining static links
Merge pull request #845 from xi/feature-instance-staticpages

Allwo to set staticpages backend for instances