Added wrapper around navbar, with default class target
Added wrapper around navbar, with default class target

New param available `navbar_wrapper_classes` in site config.

Change-Id: I914e59342ec4e73fbc84f0411bab7fde2741f84e
Signed-off-by: Martin Lowe <504e0a986396988ebec7c1694a265845da548725@eclipse-foundation.org>

EclipseFdn/solstice-hugo-theme,EclipseFdn/solstice-hugo-theme