Fix deprecations for Ember/Ember-Data 2.12

[m-basov]

Description

Since ember and ember-data 2.12 become stable there are deprecations needed to be fixed.

1. _lookupFactoryFor – link. I have added polyfill as suggested at Ember blog. Replaced with #resolveRegistration() method.
2. _shouldSerializeHasMany – link. It is now public API, but I kept both. Please let me know if you have any notices.

Some other changes:

1. I have copied ember-try scenarios from this PR to test against new ember versions so original PR may be obsolete.
2. ember-try scenarios contained wrong dependencies for ember-canary and ember-beta. I fixed them to use npm instead of bower.
3. Tests have helper to get user by username or create new. It used removed method typeMapFor, now it uses _internalModelsFor.
4. Coverage config had problems with linting because of env, I fixed it with jshint comment.

Local tests passed all scenarios and linting. Let see if it will works the same on Travis :)

EDIT.

There was problem with testem/firefox and I locked Firefox to 51 until fix.

[jamesdaniels]

LGTM. Thanks for the fixes and looking into the Firefox matter.