Updated event and speaker objects, added track object

/src/org/osuosl/ocw/Event.java: Renamed attributes to match new json structure.

/src/org/osuosl/ocw/Speaker.java: Renamed attributes to match new json structure.

/src/org/osuosl/ocw/Track.java: New object for storing conference track information
Merge pull request #11 from markholland/feature-13809

Updated event and speaker objects, added track object