fix aglio-warnings
specify expected format for PATCH endpoint
unify documentation of error responses
specify conflict cases
specify 403
improve example
specify error objects
sort and improve error id list
shrink intro on yet unspecified responses

also clarifying the meaning of collections
explicitly ban html from error messages
extend error specification

- allow collection of errors
- define ValidationError
remove definition of HTTP status codes

this list does not add more value than the standard definitions...
it is not even nearly the list of values our API will return by any
specification
change notation of multiple errors

embed them in a single error object to ease implementation of simple
clients, advanced clients wont care anyway
more clarification on embedded error infos
add HTTP 401 to MissingPermission identifier
be more precise about subject constraints
Merge remote-tracking branch 'origin/dev' into feature/specify_wp_patch

Conflicts:
	doc/apiv3-documentation.apib
remove WRITE operation where not implemented

write operation aws specified in many places that will not receive a
write-operation soon...
it will eventually be specified, but until then I'd rather have the
specs more consistent than scattering WRITE-operations throughout the
docs
make example spec-conform

also meets current implementation
Merge pull request #2056 from opf/feature/specify_wp_patch