improving looks, font-choices and type mixing: Palatino needs a scaled Helvetica

If we will have to stick with the current choice for intro.lyx and
tutorial.lyx – Palatino, Helvetica and Courier, then there is still room
for improvement:
Harmonize the x-heights.
An example for mixing Palatino and Helvetica is found here:
https://designshack.net/articles/typography/mixing-typefaces-tips-and-techniques/
 also:
http://create.adobe.com/2013/12/1/eight_tips_for_combining_typefaces.html

That would suggest something like scaling the LaTeX-Helvetica-Clone to
84-92%, 87% being my choice.
However, in 2.3-alpha, Courier's scaling option is greyed out?
(And Courier is an awful font in general but it is too skinny and runs
much too wide in this context also.)

This harmonization of x-heights will not only help with overall
uniformity and better looking documents on a line by line and page by
page basis. It will also give LaTeX a bit more room to play with
line-breaking so that incidents of margin violations in the docs might
be reduced.

Speaking of it: if the format of the docs will from now on be for 2.3
only, then the new microtype feature should be turned on by default.

greetings
Mike