"Debug" user rights

Allows creation of a user id which can view the debug tab items
printImageData() should use get_language_string() to cover multilingual content fields.
Of course even better: printImageData should use getImageData() that already covers multilingual correctly.
Better save than sorry…
Merge remote-tracking branch 'upstream/master' into upstream

Note:

Changes for cookie handling NOT merged forward as they are not corrrect.
1. Sanitization should only occur on INPUT, so not on parameters
2. The contents of a cookie is not restricted to plain text so this change will kill some cookies.

If the consumer of a cookie needs to output the results or store them in a database, they need to
be encoded or quoted appropriately.

Conflicts:
	zp-core/template-functions.php
debug rights applied to debug tab
Fix #833
and another one
delete cookie feature
Merge remote-tracking branch 'upstream/master' into upstream
Merge pull request #43 from sbillard/master

Upstream merge and delete cookie feature