[2.x] Support both Alpine V2 and V3

[calebporzio]

Problem scenario:

• Someone updates Jetstream to the latest version that supports Alpine V3
• They don't update their Alpine version to V3 (because package.json/app.js doesn't get automatically updated)
• Jetsream is now broken in the following two ways:
  • The top right menu doesn't work because it uses @click.outside which is new in V3
    
  • The little "Saved." indicator doesn't transition out because it uses x-transition... which is new in V3
    

Solution:

• Use .away instead of .outside - they are aliases and both exist in V2 and V3
• Include the legacy x-show.transition... as well as the new x-transition... helpers. Each will work on their respective versions without causing breakages.

After this PR, all Jetsream stubs will be upgrade safe and support any version of Alpine a project is using.

[driesvints]

Thanks @calebporzio. We can probably move to v3 entirely in Jetstream v3 (master branch). Once this PR is merged and merged into master we can do the changes for v3 there.

[calebporzio]

Ok, will PR - thanks @driesvints!

[calebporzio]

Looking at master: looks like I don't have to.

[driesvints]

@calebporzio I just merged 2.x into master 👍