FPCommand: convert newlines before saving

Commands submitted via the web form may end up with \r\n newlines,
which breaks bash scripts. This converts \r\n to \n at the time the
data is saved to the database.

Fixes #6512.
FPCommand form: Only display enabled verification/event commands

Previously the filtering would display *all* of these commands, which
means every older revision would be in the dropdown.

Fixes #6512.