[IMP] devtools: add __owl__ access.

[SimonGenin]

To be able to make devtools, we need access to the owl variable on a component. It contains most of the information a devtool may required.

Just like in Vue js, we attach it to the HTMLElement of a component.

For its update, we use the method patched. On each patched call, a new owl is provided.

[SimonGenin]

@ged-odoo I'm interested in your opinion. Here's where I took inspiration: Dans vue js

[SimonGenin]

I improved it a bit already with the help of Lucas.

[SimonGenin]

/!\ It added a circular dependency. Needs to be fixed somehow.