New Patterns page for using factories

[jwasilgeo]

Add a new Patterns page to describe how an Angular1 factory can be used to share state, to house esriLoader.require, etc.

See discussion in #284, and also slide 69 from the 2016 dev summit presentation which starts to touch on these topics.

I think this Patterns page should be added (and modified as necessary) to both angular-esri-map v1 and v2.

[jwasilgeo]

for v2 this is underway, but don't forget to:

• make a new test page
• write e2e tests for the test page
• make a new patterns page
• fill the patterns page with super content
• deploy to gh-pages after PR review
• then, do it all again for v1 branch (after a PR review for this into v2 master branch)