Now this class can accept '.' namespaces delimiter, which is used in
python. Changed behavior a bit: if namespaces disabled, error message
for 'Namespace:Widget' now is 'The class name contains invalid
characters' instead of 'The class name must not contain namespace
delimiters'. Error message for 'Namespace::Widget' not changed.

Change-Id: I45283ca2002957552375419f1cf3137632dcacdb
Reviewed-by: hjk <qthjk@ovi.com>