add getDijit promise helper, and test case

This adds a promise helper to simplify the boilerplate for writing Dijit functional tests.

I wasn't sure how to properly write the test for this without pulling in Dijit, so I wrote the initial test against the CDN which is probably wrong, so I could use guidance on that. In that context, I also wasn't sure what the appropriate values would be for setting timeouts, so I could use guidance there as well.
Yes, intentionally so (to reduce boilerplate in tests). Ideally, getProperty would make a call to get, or a shared common method, but I was unable to wrap my head around how to get that to work properly, with the combination of remotes, async (callbacks and promises), I hit my head on the wall for a few hours and decided to go with simple/slightly redundant to provide some syntactic sugar, rather than having to type 3 extra lines each time you need a property.

My goal with all of this is to try and make the mechanisms for accessing things with Dijit analogous in the approach for an end user to accessing a node by CSS selector.