Integrate the annotate extension

[twitwi]

• integrate the deck.annotate.js, properly keeping the git history,
• check that it seems to work as is
• check/adapt the toolbox style
• check/adapt the behavior due to the fit extension
• make the resolution of the canvas configurable (if not already)
• have one canvas per top-level slide
• improve performance by not redrawing everything every time and/or throttling the line.push
• refix undo/redo with new backbuffer
• make it sure that logs allow to replay
• make the extension clone-aware so that it is replicated to all clones
• review binding so that they do not conflict (e.g. with clone) ⇒ actually, it would be better to #20 (can take inspiration from the code in annotate btw)
• make use of number keys to switch between colors and tools