[request] rename algebraic mode to linear algebraic or plainText

[retoa]

Normally (and historically) the pocket calculator input methods are defined as:

-CHN chain operation system: it does not recognize operation priority
-AOS algebraic operation system: it recognize operation priority
-RPN reverse polish notation
-textbook (pretty print)

So I don't think we have to invent something new and use names that are twice so long as the ones universally used.

imho textbook, algebraic and RPN are the good names for the entry method.