[WIP] Modify rectangle interaction

[jlap]

This commit adds the modify rectangle interaction, along with an example of how it works.

The interactions has two layers, one layers with the points which you can drag, and a second one with the polygon that represents the box.

A live example is available here:
http://adube.github.io/ngeo/modify-rectangle/examples/modifyrectangle.html

However, there is still missing a way of knowing you can interact with the rectangle, I was thinking of either a hover effect in the style, or a different cursor pointer, but I wanted to hear some opinions before taking action. With the modify circle, what was done is the point only appears when you hover the circle, but for the rectangles, I went with the spec, where we can see all four corners of the rectangle.

I see three solutions for this:

• Changing the cursor on hover
• Changing the style on hover
• Only display the point on hover (like the modify circle)

I'd appreciate some opinions, @fgravin ! You can check out the code if you want, above changes aren't going to be huge, I'd appreciate it just to make sure this is all on the right track.

[fgravin]

Ok very good.
For the style, the modify Interaction already has a style to display Vertices.
Best option is that the hover on vertices highligh the corner.

[jlap]

@fgravin what do you think of this?: http://adube.github.io/ngeo/modify-rectangle/examples/modifyrectangle.html

[fgravin]

Very good.
I merge it, you'll work back on it if needed.
Please integrate it in drawFeature example, with the Vertex Style.
Thanks @jlap