As discussed in home-assistant/operating-system#1683, the old "HomeMatic CCU" add-on in this repository is going to be retired/flagged as being obsolete in favor of the much more advanced third-party RaspberryMatic CCU. See also the RaspberryMatic HomeAssistant Add-on Documentation.

Therefore, this PR implements the following changes:

• removes the subsystem=tty device filter type allowing to specify an arbitrary device node for connecting the HmIP-RFUSB device which will require a different non-tty device node /dev/raw-uart to be used with an upcoming HAos update. This should allow users (who cannot immediately migrate to the new add-on) to continue using the old-style add-on.
• adds a createBackup.sh script and a patched version of the cp_security.cgi WebUI file which both are internally used to generate CCU compatible *.sbk system backup files which will contain all main configuration files required. These *.sbk backup files can then be restored within RaspberryMatic so that existing HomeMatic CCU add-on users can more easily migrate to the new add-on
• adds some warnings to the major README, CHANGELOG and DOCS markdown files to get still existing users of the old homematic add-on notified about the fact that the old homematic add-on is dropped in favor of the new RaspberryMatic CCU add-on.