Enable enlarge image in ImageInnotater

[satosisotas]

Currently the width and height property in the ImageInnotation subclass are effective only if the canvas size is smaller than source image.
I would like to enlarge source image if there are no problems.

In imagewidget.js

			if (wantwidth !== undefined && wantwidth > 0) {
				self.usewidth = wantwidth;
				self.canvas.setAttribute('width', wantwidth.toString());

                                // Disabling zoom if canvas width is larger than source image width.
                                // Therefore only shrinking is possible.
				if (wantwidth > self.imgel.width) {
					self.usewidth = self.imgel.width;
					self.zoom = 1.0;
				}
				else {
					self.usewidth = wantwidth;
					self.zoom = wantwidth / self.imgel.width;
				}
			}