[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
Also, as is, the params listed in the docs are incorrect.