LibWeb keeps growing and the Web namespace is filling up fast.
Let's put DOM stuff into Web::DOM, just like we already started doing
with SVG stuff in Web::SVG.
We still have to hand-write a function to turn an Event& into a wrapper
but this is still a hue improvement. Eventually we'll find a way to
auto-generate that function as well.
This patch adds the Event base class, along with a MouseEvent subclass.
We now dispatch MouseEvent objects for mousedown, mouseup and mousemove
and these objects have the .offsetX and .offsetY properties.
Both of those properties are hard-coded at the moment. This will be
fixed in the next patch. :^)
