Feren OS Major Update support

[dominichayesferen]

Technically, it would be good to implement support for this in 1.0 as it'd likely dictate a lot about how the modules might work.

• Handling EOL'd/moved installed items #14
• Figure out what module to do this with - custom module type for 'system version upgraders' that can bring out tasks of its own and task modules for other modules, and can only be one hardcoded value like GUI?
• Figure out how to store package changes required (per module?), transitions required, etc.
• Make the major update its own task when preparing, or a system update task?
• Ultimate goal: Recreate Feren OS 20.04-based -> 22.04-based in this method as a test example

[dominichayesferen]

Upon further consideration, this will likely just take the form of a special hardcoded ID itemmgmt module that:

• Requires Superuser on its main source
• Cannot be managed as a source in sources
• Has its own version of the API where it can declare stuff like items to migrate to other sources, EOLs, etc. inside of the changes dialog
• Add any task in a group, irrespective of module nor source
• Declare requirement of any source from any module, as usual
• Remove sources if needed
• Have its own status messages on its task
• Force itself to installonshutdown state