Menu: use LinkTitle instead of Title

[thaJeztah]

LinkTitle allows overriding the title to use in menus in a page's front-matter. For example:

title: This is the title of the page
linktitle: menu title

It a linktitle is defined in the page's front-matter, it will be used as title in the menu. Pages that do not have a linktitle configured will use the title instead (see https://gohugo.io/content-management/front-matter/).

[thaJeztah]

@thingsym ptal

[zybex86]

I believe that there is also one problem with the Home menu item as it is ALWAYS added to a slide-menu which would be nice when it wasn't.