Stop marking buffer as read when full-screen message compose interface is open

In brief

• Don't mark buffers as read while the message compose interface is expanded
  • Makes it possible to notice new messages, including those which would change one's reply
  • Might be desirable enough to not need to become another setting
  • Tablet UI may be different (not tested)

Example

1. Open a private message with a user you can send messages from, or visit a channel you have another account in
   • Applies to both use-cases
2. Swipe up the message compose box to cover the list of chat messages
3. Imagine you're spending a long time composing a message
4. From the other user send a private message or channel highlight to this user
5. Observe how Quasseldroid handles the new message/highlight
6. Swipe down the message compose box to reveal the list of chat messages
7. Imagine you've received a message that would have changed your reply significantly

Before

Quasseldroid marks the incoming messages as read, despite not showing the message or any notification. Time might be wasted.

After

Quasseldroid won't mark messages as read, and won't move the marker line while the compose box is expanded. Once the compose box is no longer expanded, Quasseldroid resumes marking the active buffer as read.

Hypothetical conversation

[1:23 pm] <someNick> digitalcircuit: What was your reasoning behind this change?

starts writing a lengthy reply in the expanded message compose interface

[1:25 pm] <someNick> digitalcircuit: Nevermind, I found your past message