Add support for NanoGong activity

Compatible with NanoGong version 4.2.3.1 (Moodle version #: 2013011400)
Merge pull request #4 from mattrice/master

Add support for NanoGong activity
"Expect competed on" display accurately in editdates report, #7772
Fix deprectated get_context_instance.
Update version and readme for the 2.2 release.