Add compile time flag for disabling CV screen

[Xenoamor]

This would be handy for those of us who only want the merged screen

[kanflo]

Good idea. On a similar topic I have been thinking we could use some kind of ./configure like step that would set the font, font colors and desired functions. With this config a git pull && make would build the latest and greatest according to one's configuration.

[sercona]

I did some ugly hacks just to remove the CV/CC indicators from the screen since the use-case for my builds are for non-tech users and not having those telltales means less questions to have to answer ;)

I'm also thinking about making the default screen show the set-value and not the actual dac value. I think when enable-mode is off, then its the set-value that is shown for voltage, but I prefer to always see that has there been any thought to an option to show it that way?