Don't carbon copy messages with <no-copy/> hint

Honor the <no-copy/> hint defined in XEP-0334.
Don't store messages with <no-store/> hint

Honor the <no-store/> hint defined in XEP-0334.
Don't log MUC messages with <no-store/> hint

Honor the <no-store/> and <no-permanent-store/> hints defined in
XEP-0334.
Merge pull request #207 from weiss/xep-0334

Honor XEP-0334: Message Processing Hints