Force underscore after decamelizing typeKey.

Type key is not always camelized, ember-jj-abrams-resolver for example
uses dasherized type keys.
Normalize typeNames when comparing against typeKey.
Don't assume that factory.typeKey is always camelized.
Merge pull request #1652 from abuiles/camelize-in-pathForType

Force underscore in pathForType - don't assume typeKey to be camelized.