Rework MessageDelegate to be mostly a cpp class. This allows us to only load the components that are actually needed saving memory.
In testing using memtest it saved ~30% versus the current implementation.
Make `DelegateSizeHelper` take a `QQuickItem` rather than a width value and move `TimelineDelegate` to use it rather than duplicting the code.
This requires the creation of `LibNeoChat` so that both the main and timeline modules can get access to the class.
Note: ideally more stuff will go into `LibNeoChat` but it turns out our dependencies are kinda spaghetti like and so will take some untangling.
There are 2 main reason for doing this:
1. Because I can, I wanted to see if I could do it
2. It gets rid of the janky qml re parenting stuff so should be faster.
