Allow to use x instead of * for multiplication

FEATURE: 350066
FIXED-IN: 5.20

This will allow us to run queries like:
4x4
4x4.2
4x,2

But if we explicitly want the x to be interpreted as a variable by qalculate we can run:
=4x*4

This will work with and without qaclulate available.

@ngraham @davidedmundson And maybe @cfeck since you commented on the bug right when I was typing this description :-).