Bump Ember-Data to 2.14

[clekstro]

Includes @drogus' workaround for unexpected unloadRecord behavior.

[clekstro]

It looks like we are stuck on 2.12.2 for the time being. The unloadRecord issue is fixed, but upgrading has brought in several other re-render errors that aren't present in 2.12.2. It's possible that we'd need to change something on our end, but I started digging into it and don't see exactly where the issue would be coming from. Came across this issue and it seems like a different Ember-Data bug.

EDIT: corrected the version we're on (2.12.2)

[clekstro]

Unfortunately, emberjs/data#5119 doesn't appear to have fixed this. But oddly enough, I'm only seeing the issue in our test suite.

[clekstro]

We've since upgraded to 2.15 in #1307, closing.