Add quiet flag to math command

feat: For some automation tasks it would be nice to enter the interactive math mode without any welcome text. For this we could use a -q/--quiet flag to silence this (similar to R).

current

me:~# math
Ion's integrated calculator
Type in expressions to have them evaluated.
Type "help" for help.
ion-math: 

change

me:~# math -q
ion-math: