Update Docs Styling & Nav

[yeldarby]

Description

This is a first pass at updating the nav architecture and styling of the docs in preparation for a major revamp.

Changes:

• Updating logo, favicon, fonts & colors to match our brand
• Updates homepage to lie outside of nav hierarchy
  • Fixes mobile nav (before it was completely unclear you landed in a sub-nav & had to click the back arrow)
  • Hides sidebar to set the index up to be a better landing page
• Nav hierarchy update (renames the legacy "Roboflow Inference" section to "Models" to more closely match what it is & moves some pages around to support that)
• Updated styling (font sizes, margin, padding), simplified header w/o giant dark-mode toggle button

Homepage Before:

Homepage After:

Inner Page Before:

Inner Page After:

Mobile Nav (From Homepage) Before:

Mobile Nav (From Homepage) After:

Type of change

• New feature (non-breaking change which adds functionality)

How has this change been tested, please provide a testcase or example of how you tested the change?

Non-functional change; previewed via local docs server.

Any specific deployment considerations

Just docs.

Docs

• This is a docs change.

[hansent]

lgtm