Make some windows of a Tab class unique for that tab
For example, all UserList of all MucTab have the same size and
And all PrivateInfoWin of all PrivateConversationTab do.
These Win instances should be unique and kept as a class attribute (and not instance attribute). This would save some memory and some work when resize() is called.
Maybe built_lines should not be kept in the TextWindows as well, but in the tab, and passed at each refresh. This way we could make only one TextWindows, and save even memory and time.