Improve validation around params changing

[alexlafroscia]

• Figure out how to actually write tests for errors being thrown
• Un-skip skipped tests
• Make sure that the following attributes all throw an error when changed
  • step
    • name
  • step-manager
    • initialStep
    • linear

[alexlafroscia]

Related issue: workmanw/ember-qunit-assert-helpers#18

[alexlafroscia]

On second though, maybe it should just be an Ember.warn rather than an Ember.assert. In reality, it's not that bad if initialStep or linear change, it should just be made really clear that changing those values after the initial render will not do anything.

step.name is a little more complex. In reality, the state machine could support updating names of steps, but it's probably not that useful. However, I'm going to support removing steps, so handling renames actually wouldn't be that hard.

[alexlafroscia]

Once this is resolved, it makes most sense to approach argument validation that way:

ember-decorators/argument#65