Signed-off-by: Francis Storr <francis.storr@intel.com>

This update:
1. Restores Roboto and Lato fonts for most body copy, leaving Intel One Mono for code samples.
2. Adds colors (in `colors.css`)
3. Adds a new `accessibility_overrides.css` file containing CSS that improves the accessibility of the documentation and, where possible, Read The Docs. These updates remediate numerous non-conforming WCAG 2.x Level AA bugs. The use of a separate file for this hopefully makes these changes easier to manage and less likely to be accessibility overwritten in the future.

Closes securefederatedai#848

Signed-off-by: Francis Storr <francis.storr@intel.com>

…bility

Color contrast updates for accessibility
- update generic `a` element
- update color of links in the toggle-able read-the-docs panel
- update the color of the text in search results
- update the color of notes headers

Signed-off-by: Francis Storr <francis.storr@intel.com>