Shibboleth: keep the cookie from the wizard to the ShibolethCredentials

Otherwise the user is asked twice for autentication on first sync.

Fixes https://github.com/owncloud/enterprise/issues/193
Documentation update from Mark.
Remove version suffix, final release 1.6.1
Merge remote-tracking branch 'origin/1.6'

Conflicts:
	VERSION.cmake
	doc/building.rst