Rename variables none/empty to isNone/isEmpty

[karlguillotte]

Really small changes, this PR renames the variables:

• none to isNone
• empty to isEmpty

It makes the code easier to read.

[Floby]

Hello,
these changes make any business logic item using an isEmpty property break the ember-data layer.
isEmpty is a very common name for anything else than lazy loaded records. I suggest a name change or a warning when defining such a property on models.

[bradleypriest]

This should have nothing to do with defining isEmpty on a model. It's literally just changing variable names within a closure.
Your issue must be due to something else.

[Floby]

You're right, I'll open its own issue.