[WIP]: Update Reflection component to v2

Part of the operation for speeding phpDocumentor up is removing the extra step of putting the parsed contents in Descriptors using Reflection objects. Instead Descriptors will be assembled directly from the parsed contents.

In this PR I have removed all descriptors as they have been moved to the Reflection Component and changed all files to match the updated API for the Descriptors.

In addition to this the minimum PHP version is updated to 5.4 to match the new Reflection component
That's [Traversable](http://php.net/Traversable). An object doesn't have to implement one in order to implement the other.