* adding work and organization for docs

* Summary of changes

- removed rst file from css folder
- added substitutions to conf file so folks don't have to type out the whole name
- added branding notice so link in footer works
- added glossary so we can have a place for terms relative to libngraph
- added placeholder for MXNet and TF frontend under new section
- cleaned up api page

* Fix code fencing error and indentation issue causing build to throw error

* adding MXNet integration guide details and other miscellaneous structure

* fix unicode error in rst epilog

* testing with unicode marker for rst_epilog string

* replace api scaffolding with TODO to avoid breaking Jenkins