Conversion fixes -- ALSO REVIEW: all of Appendix E

* Addressed some invalid 0.9 statements
* Added conversion for non-URI extension keys

Note!: Appendix E got merged before it was fully reviewed, please have a look at the entire appendix if  you haven't yet.

Some points for discussion brought up so far:
* Invalid 0.9 statements, especially those using verbs or activity types not defined in the ADL list. (has this been sufficiently / properly addrssed?)
* agents that have a first name and last name - should name be calculated?
* should use of "urn:expapi:0.9:activities:" be restricted to converted 0.9 statements.
* are we OK with using a urn: prefix with our made-up post-urn scheme? would we rather use a URL that won't resolve?