[Seaside] javascript canvas

[Yan Laporte]

I finally got around and implemented this, it wasn't difficult at all.
Right now its crude and closely follows what is available in the
javascript canvas itself, it's pen based and could most likely be
improved. It does allow to use few useful existing squeak classes such
as Point, Rectangle, Path (subclasses don't work tough) and Color.

Its useful for a few things such as moving image composition to the
client side, doing your own special web charts in smalltalk  etc. etc.

>> Now, what I meant by classes to make this easier would be to allow
>> something along the lines of:
>> |myCanvas|
>> ...
>> myCanvas:=html canvas width:100;height:10.
>> (DrawingContext on:myCanvas)
>>     fillStyle:ColorBlue;
>>     fillRect:(10 at 10 extent:40 at 40).