Assure function can be found.

Function is_valid_firmware_file has to be found from other files.
Added security checks if firmware file is valid.

Check for file name endings and size.
Added delete option

Usb3 camera firmware can now be deleted through the command:

firmware-update -d <serial> --delete

This option is undocumented
Added ram firmware write for usb3 cameras.

Cameras that identify as Cypress can now receive firmware files that
will be written to RAM. This allows a complete restoration of camera in
the case of damaged firmware images.
Cleanup

Indentation, spelling, ordering, etc.