Use Keys file, added keys for htpasswd US.

Changed the htpasswd key from .file to .userfile.
Added keys to gitblit.properties file, relying on the build to include them in the Keys class. Swicthed to using Keys class in code.
Implement overriding local accounts with htpassd file.

Add option to overrride and overwrite an existing local account if the account is found as an external account, too.