Jumbotron: remove the hard-coded font-size from jumbotron.less and moved it into variables.less where other .font-size-xxxxx things now live.
The Jumbotron font-size LESS variable now conforms to the '@{bootstrapClass}-font-size' naming scheme.
The customizer now displays and collects the new Jumbotron font-size LESS variable
Good catch by @juthilo - omitted the modified  in a prior commit.
Merge pull request #10949 from StevenBlack/jumbotron.fontsize

Jumbotron: remove the hard-coded font-size from jumbotron.less and moved...