Renamed SimpleResult to Result

* Renamed SimpleResult to Result
* Removed all deprecated result types
* Merged WithHeaders into Result since it only existed for the purpose of sharing functionality between PlainResult AsyncResult
* Introduced SimpleResult type alias and object as deprecated for the purpose of easing migration
* Updated all Java helper code that didn't compile as a result of these changes

However, I did NOT change any code that used SimpleResult to now use Result.  This includes Play core code, documentation, tests, and samples.  The reason for not doing this yet was to prove that the SimpleResult type alias and object apply and unapply methods were enough to ensure source compatibility with all existing code.