Cleaning up libcosmic

[Adam-Cosner]

Hi, I think it would be worth discussing some quality of life maintenance for libcosmic. Right now, there are some issues with the developer experience of using libcosmic and, compared to iced itself, libcosmic has become kind of a Frankenstein patchwork of abstractions with multiple structural inconsistencies. I plan on submitting some PRs to fix a few headache things I've noticed. Here are a list of some things I think need some work:

• The libcosmic book needs a lot of work
• Better code documentation is desperately needed, and it also needs to show all of the feature-gated user-facing modules (cctk and process being major ones)
• Possibly separating widgets by category or unifying the two separate design philosophies of widgets: model-object driven vs procedural. Iced itself has a policy that all widgets need to be procedurally built, but libcosmic has multiple widgets that operate via a Model object that is passed in, which handles layout of certain widgets. The two are completely separate philosophies and in the interest of cleanliness, it might be worth it to separate all of the model-driven ones into their own separate submodule of cosmic::widget
• Some cargo features are either unnecessary or completely random and the README section is outdated (i.e. winit and wayland are not conflicted)
• Figuring out a better solution for the "cosmic::cosmic_" modules, as, while I understand that they do serve different purposes, think of how someone new to the library would see it. They would have to dig into the documentation and even the code in some scenarios to figure out the difference between cosmic::theme and cosmic::cosmic_theme, and even then it's sometimes unclear. Not even to mention that the repeated use of the word "cosmic" just kind of looks odd grammatically.
• Possibly looking at re-exporting/abstracting iced's components separately so that libcosmic no longer needs to expose the underlying iced API
• Various modules being in odd places (why is keyboard_nav on the top level?)
• Update the prelude module to import more things that are commonly used (like row() and column())

If you have any more suggestions or odd things you've noticed about the developer experience, feel free to comment.

[Adam-Cosner]

Some other things I thought of:

• Publishing to crates.io and moving to tagged releases now that COSMIC itself is now seeing proper versioned releases
• Potentially making automated actions to generate draft PRs in the official COSMIC apps whenever libcosmic gets a tagged release
• Contribution guidelines with things like documentation requirements and architectural patterns
• Utilizing more Rust attributes to make the code more robust
• Getting rid of all of those compile warnings