[WIP] Remove jQuery guide

[simonihmig]

This is a first draft for the necessary changes as per RFC 294:

• adds a "Remove jQuery" guide
• removes this.$() references from component guide in favor of this.element and native DOM

Please double check, as I am not a native speaker! 😬

And don't merge this yet, unless the RFC is fully implemented

[jenweber]

@simonihmig I made a few wording changes in source/addons-and-dependencies/removing-jquery.md

Looks good so far!

[simonihmig]

@jenweber thanks! 👍

[sivakumar-kailasam]

Thanks for taking the time to contribute to this project. We’re in the process of switching from middleman to an ember app to make it easy for contribution.

We’re closing issue since its been open for too long without progress / it needs more discussion which is probably better had via a new PR in the new app. (sorry about that)

If this PR has changes to the content of guides please raise a PR to https://github.com/ember-learn/guides-source. If the change is to the guides viewer (i.e., the app) then please raise a PR in https://github.com/ember-learn/guides-app/. The READMEs and contributing.md guidelines of those projects will familiarize you with the new process. Let us know if you have any questions!

PS: this is a standard msg we're using across such PRs