Add the variable $include-html-top-bar-classes.

Add the variable $include-html-top-bar-classes.
Replaced $include-html-nav-classes by $include-html-top-bar-classes

Replaced $include-html-nav-classes by $include-html-top-bar-classes. Also added "!= false" to be consistent with the rest of the .scss-files.
Merge pull request #2367 from MekZii/master

Added $include-html-top-bar-classes