Move links out of navbar and into sidebar / other docs.

[TimMonko]

References and relevant issues

Closes #615. Follow up of #610. Remake of #617 because I got confused with the commit history and merging

Description

I think the navbar is a bit too cluttered due to the 'More' section being propagated to the sidebar in smaller width screens (and generally being finnicky)

1. Moves 3 lower-value (I still love them) links out of the navbar: blog, zulip chat, and workshop template
2. Moves blog to homepage sidebar (confirms there is a link to blog in community)
3. Moves workshop template link to Workshops page in Usage, also adds a link to Contributing index
4. Removes zulip link in favor of presence in homepage sidebar and presence in footer. If we want to keep this in header we should move the footer link up to the header in theme
5. Adds troubleshooting link to homepage sidebar (check that this is internally referenced correctly, I can't do https://napari.org/troubleshooting.html/ like I can for other internal refs, it 404s)

[DragaDoncila]

Looks good to me! Thanks @TimMonko

[melissawm]

I like this more than I thought I would. I like the visibility this gives to important shortcuts.

This may need some discussion at the docs WG though!

Screenshot for ease of review: