Updated static media documentation.

Added sphinxcontrib-httpdomain to requirements.txt.  This is needed to
build the documentation.
Move the documentation requirements to their own files

In order to make things work on readthedocs, I think we need to point
them to a requirements file so that sphinxcontrib-httpdomain gets
installed.  Making a documentation-specific requirements file seems
like a good way to do this.
Updated documentation to eliminate sphinx errors