messages can now be 'opened' as floating windows over the chat (at most one open at a given time)
Merge branch 'master' into win
central mwindow can be reduced to a tab on one on the 4 sides of the window
a mwin tab whose content has changed (including on a ludo move) changes color
trying to make the **exactly 3 coins** rule clearer in Tribo
Fixed a few bugs in markdown to html formater