Also made the TextAnnotation classes conform better to VTK-m coding
style. Specifically, changed the order of words in subclass names (e.g.
TextAnnotationBillboard instead of BillboardTextAnnotation) and broke
out each subclass into its own header/source files.
I have noticed at least on my windows machine that source code that uses
the rendering package is taking a long time to compile. The rendering
library does not rely much on templates and more on virtual methods.
Thus, it is a good candidate for moving to a library so that it need be
compiled only once.
This sets up the configure scripts to create the library. There is also
a simple port of one class to the library. More will follow.
