Add grunt-ember-templates build against latest ember

[andyhot]

We could have a branch that is always built against the latest ember version.

Then we can setup travis to run the tests once per day. That way we can catch regressions to the ember-template-compiler.js much earlier (and even report them to ember)

Here's my current plan of attack:

• Add a folder test/expected/latest
• The expected templates inside test/expected/latest can contain a <LATEST> placeholder that is substituted with the ember-template-compiler version before they are compared with the actual results (but I noticed that since ember#2.10 the version is NOT included in the generated artifacts, so I consider this step optional)
• Add the testEmberLatest task in Gruntfile.js
• Find out how to trigger travis once per day (or even after new commits in ember)

[andyhot]

I'll have time to tackle this later tonight but if someone wants to take over, let me know :)

[zoltan-nz]

@andyhot great idea. Don't hesitate to send a pull request when you have a few free minutes to deal with this mission. Really appreciate your help.