new homepage layout and Mosaic streaming document

- Removed 3 column homepage view since it breaks the "Site" navigation
  that `sphinx-bootstrap-theme' expects.

- Removed homepage images for now.

- Renamed directories to match new TOC naming schema.

- Reverse ordered TOC to appeal to advanced users.

- Added Mosaic streaming document.
ignore emacs files
drop redundant contents (already in `Page' menu)