Proposal: Adding a Plasma Login Manager

[David Edmundson]

As discussed in Plasma meetings and Akademy's, Oliver Beard and I have
been working on incubating SDDM into Plasma whilst also providing a
more coherent Plasma experience.

This has been implemented as two new repositories:

https://invent.kde.org/davidedmundson/plasma-login-manager) a
continuation of SDDM with full history.
https://invent.kde.org/davidedmundson/plasma-login for front end and KCM code.

It doesn't have to stay that way. The front end was separate because I
tried using greetd first. Then the backend is separate as it has SDDM
history imported. We can choose to merge them, or put the front end in
plasma-workspace. I'm not sure what we want.

It's not quite at a stage ready for official kdereview, but ready for
development.

I've written up a blog post, because social media will pick this up
this thread anyway, and I wanted to explain some previous discussions
without rehashing here:
https://blog.davidedmundson.co.uk/blog/a-roadmap-for-a-modern-plasma-login-manager/

David