SOLIDUI: add overflow to nav menu for mobile

[jesscmoore]

Description

Add an overflow option to nav menu, which moves those menu items to a More button in mobile or narrow displays.

Why

So that as a user I don't have a crowded bottom nav bar on mobile apps.

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• On mobile/narrow screens, the overflow menu items show in a More button.

Screenshots

Eg The 7 buttons now in the menu of Podmail is too many for mobile platforms. As a developer I want to set which will appear in the More button, and which will be shown.