Optimized off canvas menu script

Made sure listeners are added/removed when necessary and that events
are propagated correctly.
Fixed overflow sideway scrolling bug

There was an issue with overflow:hidden causing a weird sideways
overflow issue that’s now fixed. Added variable to set of the
$off-canvas-menu-width and $off-canvas-menu-bg.
Wrapped off canvas menu nav in HTML ID wrapper

Wrapped the nav.ua-eng-off-canvas-menu in a
#ua-eng-off-canvas-menu-wrapper in an attempt to help with scrolling
issue.
Moved the main menu to the framework

Made some main menu variables and made SCSS file called from child
theme SCSS file.