[BUGFIX] error when trailing slash present in argument to generator

This PR provides a hook inside the Blueprint install function that by default throws and error when there is a trailing slash in the argument to `ember generate`.  This can be overridden within each individual blueprint by overriding the normalizeEntityName function inside the constructor for that blueprint.

Let me know what you think.

resolves #1164
I believe that `ui` is not needed, it is set as a prop on the blueprint instance when instantiated, so even if a downstream blueprint wanted it, it would just use `this.ui`.