theme: revise the use of elements in the top bar

[yhontyk]

There are a few issues I have experienced with the default theme that we use.

1. Target links in the bar tend to be duplicated unless smb manually fiddles with the bar on the project level:

2. I personally(!) tend to expect the top-left corner link to lead be to the root of the website/landing page. I make the mistake quite often out of some habitual mental model so I think it's worth looking into it if there is a better way to guide users to the root link rather than the link that would lead to the parent project/marketing page/whatever. Discussion here (internal): https://chat.canonical.com/canonical/pl/4aqpwwhbqbf9dbi81gibz8b3to

[medubelko]

Thanks for pointing this out, @yhontyk. It's definitely an inconsistent pattern across our sets.

There are two cases:

• In sets without a marketing site, the button links to nowhere. That's a bug we can easily fix.
• In sets with a marketing site, the button links to it. This is redundant with the first item in the nav bar. Changing this is also easy, but we'll need assent. It has the potential to affect clickthrough performance in marketing.

As an aside, in the current state of the Ulwazi theme, the parent website page is clearly distinct, so this will be organically resolved when we adopt it.