Support multiple web views simultaneously

[igalia]

Support multiple web views simultaneously

[aperezdc]

This is being worked on in the branch devel/multiple-views. It still needs work, but it is already in an usable state.

Lots of thanks to @psaavedra and @csaavedra who have been contributing towards getting this done! 💪

[aperezdc]

The changes in the devel/multiple-views branch are too many for a single PR that would apply to master—I tried a few times to rebase but it is a Herculean task. I am going to try instead moving things slowly into master to make it slowly morph into shape, let's see how that goes.

[aperezdc]

While there has been some work to slowly move this code over to the main branch, it's not there yet, so I am changing the milestone to 0.14 🙃

[aperezdc]

The infrastructure needed for this is now merged the master branch, so let's close this and for the remaining issues we can open new issues.