New Design and UX for Message Bubbles

While working on the Dark Theme with @grote we discovered that the message bubble colors required changes made to PNG drawables, split into 9 pieces (for dark, light, incoming, outgoing and system notices). This makes it quite rough to work with and is time consuming when it comes to updating changes. Also, the current design is an old message bubble pattern and one can see from Facebook or Telegram that a more rounded approach might be more suitable: