Improved validation and other features of Save

Save now closes the ostream. It didn't before and it's a wonder why it never crashed.

The comment and separator validation has been improved to disallow - + and e as they're part of the scientific notation. the separator = comment check is now bundled into the comment's regex check.

Spectra min/max have now got a positive check.

Headers now use the specified spearator character.

Refs #7732