Update home page layout
Rename "Slide Atlas" -> "SlideAtlas"
Replace home page image with a smaller version

The new image is downsampled to 488x364, which is the maximum size shown
in a 5-column layout on a desktop viewport. The new image is ~25% of the
file size of the original, making it faster to load.

Fixes #15.
Merge branch 'page_ui_refinements'

* page_ui_refinements:
  Replace home page image with a smaller version
  Rename "Slide Atlas" -> "SlideAtlas"
  Update home page layout
Improve site version reporting to be more robust

Adds the ability to read site version from a version.txt file, if it
exists and Git version checking fails.

Fixes #13.
Merge branch 'site_version'

* site_version:
  Improve site version reporting to be more robust