Redraw shapes when resizing the HTML5 client

Only redrawing shapes that were loaded when the HTML5 started. Shapes
drawn before are not being saved in the arrays yet and so are not being
redraw when resizing (they disappear).
Add WhiteboardRectModel to clean up WhiteboardPaperModel

First version, there are still things that should be moved from
WhiteboardPaperModel to it.
Round borders for rects and pencil in the HTML5 whiteboard

Makes the drawings more similar to the drawings in the flash client.
Add WhiteboardLineModel to clean up WhiteboardPaperModel

First version, there are still things that should be moved from
WhiteboardPaperModel to it.
Add WhiteboardToolModel as a base for whiteboard tools in HTML5

WhiteboardLineModel and WhiteboardRectModel already inherit from it.