ui: Side navigation tweaks

[johncowen]

This PR adds a few little amends to the new sidebar navigation:

1. Larger Consul logo
2. Use dark menus for header menus as well as side menus.
3. Remove app footer and move Consul version output to the Help menu
4. Revert unique ID usage so we can keep using the login modal id throughout the app to toggle it instead of having to pass around JS things.

[hashicorp-ci]

🤔 Double check that this PR does not require a changelog entry in the .changelog directory. Reference

[kaxcode]

[jnwright]

Looks like the color of the version needs to be changed to be the same as the section headers (ui-gray-400). Font size also should be 12px

[johncowen]

Hey @jnwright

Oh good spot! I knocked the gray on the version down a couple of notches so its equivalent to ui-gray-400.

We use relative sizes for font-sizing (not pixels), the version is 0.75rem which, in our app, equates to 12px.

Lemme know if that makes sense.

[hashicorp-ci]

🍒 If backport labels were added before merging, cherry-picking will start automatically.

To retroactively trigger a backport after merging, add backport labels and re-run https://circleci.com/gh/hashicorp/consul/332197.