OpenSystemsDevelopment / usbboot

This also resolve a startup issue CM4-S

Typo fixes from @dp111 (who obviously has too much time on his hands).

Include the new imager applications and fix the recursive File
operations to stop the installer pulling in the .git directory.

Update udev rules to use uaccess tag

Initial BETA release for secure-boot.

secure-boot adds two new sub-directory to usbboot:

* secure-boot-recovery is used to create an EEPROM signed with
  the customer's RSA private key and configures the 2711 OTP
  settings permenantely require signed boot images.
  See secure-boot-recovery/README.md
* Once secure-boot is enabled the CM4 MSD mode firmware must
  also be signed with the customer's RSA private key.
  See secure-boot-msd/README.md

N.B The revoke_devkey and program_jtag_lock are NOT enabled in
this initial BETA release.

The recommended way of granting users access to USB devices is not using GROUP="plugdev", but TAG+="uaccess":

    https://wiki.debian.org/USB/GadgetSetup

* Add 2711 bootcode and FW binaries with the 4 suffix.
* Use the device descriptor to select the correct bootcode and
  hack it so that bootcode.bin translates to bootcode4.bin on a
  Pi4 allowing the files to remain in the same directory.
* Add the latest best for recovery.bin and pieeprom.bin for CM4
* Update the installer.

Move the second stage preparation until after the device descriptor
has been retrieved because BCM2711 needs a different bootcode.bin.

If the '-d' argument specified then check for bootcode.bin in the
specified directory and don't fail over to the embedded fmem files.

Remove the default 'msd' directory and the references to /usr/share
because the behaviour conflicts with the original change to use
the fmem files.

* Do not require root privileges

Give members of plugdev group access to the usb device by udev
rules.

* Disallow requests for files outside directory

* Be more verbose about errors

* Error out if permission was denied while opening device.
* Show error if request for file containing .. was denied.

Add lintian overrides