Cleaning up the base setup and template.
[UI/Messages] Added base class.
[UI/Messages] Ensure proper margins for nested elements and the messages themselves.
[UI/Messages] Added message size variations.
[UI/Messages] Added attached messages.
[UI/Messages] Added lists within messages and updated the template.
[UI/Messages] Removed the size variations in favour of generic, global size classes within Mai/Base.
[UI/Messages] Added a message variant with an icon and starting to refactor variations into separate files.
[UI/Messages] Added colored variants.
[UI/Messages] Moved the attached and compact message variations to separate files.