feat: better left navbar response at varying heights

[jessicaschilling]

Closes ipfs/ipfs-desktop#1668 (but requires release of webui).

• Makes room for Electron window furniture (top left) vis-a-vis logo when used in IPFS Desktop
• Maintains the 640px+ (aka 40em in our height system) behavior requirement outlined in feat: add version info in nav and Status screen, tighten nav accordingly #1654: preserves display of version/revision/repo/bug-report links at nav bottom for 640+ high windows
• Enhancement: Adds a "height breakpoint" for condensing left-nav elements at windows shorter than 49em (see screenshot)
• Behavior at different heights remains unchanged if window is narrower than 60em (aka width breakpoint for moving the nav to the top of the window)

Eyeballed as OK in Web UI in Mac Chrome, Firefox, and Safari.

Gif demonstration (Mac Firefox): https://gateway.ipfs.io/ipfs/QmUiSXL2Gt1176ncuUjU8KaKuPYkWyXu3tMK2opU5BF5CZ

Quick screenshot for comparison (Desktop RC2 from here on left, full-height Mac Chrome in middle, condensed-height Mac Chrome on right):

@rafaelramalho19 may have tweaks for a cleaner approach, but as-is this doesn't substantially introduce complexity, and in return offers a cleaner left navbar experience overall.

[lidel]

Thank you! Quickly eyeballed in Electron/Desktop and looks good too.
Will cut a release to fix ipfs/ipfs-desktop#1668 tomorrow.

ps. nice side-effect: we now use em for all navbar media queries