[vendor page] Add link to Vendor page from top nav

[mrose914]

The new vendor page includes a requirement to add "For Vendors" as an option from the MobiMart homepage, specifically in the top nav.

The rationale for this change is that vendors are a significant segment in terms of users of the site and should be able to quickly access information that may be most useful to them.

Acceptance Criteria:
After this change is implemented, the top nav should read, from left to right:

• Products
• Contracts
• For vendors
• About
• Contact us

[segacy1]

Design Note: In figma, the desktop nav bar was updated so that:

• each page link has 72px between them
• there's a column of whitespace on either side of the nav content

Mobile nav discrepancies are noted in the design backlog (ex: mobile menu icon in Figma to match what's live)

Hero Graphic:
hero-graphic.zip