Fixes #12738

* Removes default max-height from .navbar-collapse (so not every navbar
will get a max-height collapse section)
* Scopes regular 340px max-height to fixed top and bottom navbars only
(those are the only ones that really need a max-height to enable
scrolling)
* Adds a landscape media query for phones to cap the max-height at
200px for fixed navbars"