Warning message standardization

[noah-schechter]

When I made the first round of copy edits I didn't take into account standardization because I was looking at things on a case by case basis. My current thinking is that minimum warnings should be "Minimum X characters.", maximum warnings should be "Maximum X characters.", and blanks should be "[Field] can't be blank."

I'll include relevant issues below.

[noah-schechter]

Though for multi-select options, the appropriate warning is going to differ more based on context.