Allow characterization as a selectable type
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.
Separate out FPR rule/command categories

This separates out FPR rules from the generic, and increasingly
inaccurate, "Normalization" category. Instead, a new category for each
of the support FPR categories is included in the sidebar. This is a
little verbose, but hopefully still clearer than the old display.

refs #6606
FPRule: add constants for usage strings
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.