OSMF SVN

Adding the missing readme file for the captioning sample app.

Commit of traits refactored as classes instead of interfaces. A trait now has a public API for clients, and a protected API that implementors can use to hook into the workflow. Lots of additional changes:
* Merge spatial and viewable traits
* Merge load and download traits
* Merge play and pause traits
* Refactor MediaTraitType to hold strings (consistent with PARB)

Note that the composition layer is currently disabled (CompositeElements only support the Audio and Buffer traits). There may also be some bugs in the area of HTML support.

Improvements to the DFXP parser, captioning sample, and a bug fix for the TemporalFacet (duration timers were not taking account of the media being paused).

Initial check-in of the captioning plugin and sample app.