Move svFSI documentation to svFSI+ repository

[mrp089]

I'll move the svfsi folder to the svFSI+ repository (see SimVascular/svFSIplus#110) to keep the documentation with the code.

First, I'll add the files to the svFSI+ documentation folder and include them in the Doxygen HTML build. Second, I will delete the files from this repository and include a link to the new documentation on the main page.