Add a custom user service using an Apache htpasswd file for
authentication.

Add a new class HtpasswdUserService which implements custom
authorization against a text file created with the Apache 'htpasswd'
program.
Moved HtpasswdUserService.java to new source directory according to new
layout after direcory reorganisation since v1.2.1.
Adjusted to Constants.EXTERNAL_ACCOUNT.
Added dependency on commons-codec:1.7
Adjust account type to use general AccountType.EXTERNAL.

Use the new AccountType.EXTERNAL which is available since v1.3.0.
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.
Adjust method comments.
Fix problem with invalid MD5 passwords.

Fix a problem where specifying a wrong password for a user that has his password stored as Apache MD5 would result in an IllegalArgumentException.
User IStoredSettings instead of Gitblit. Changed realmFile variable name.

Implemented two suggestions:
Renamed the variable realmFile to htpasswdFile.
Store the IStoredSettings passed into setup() and use that instead of Gitblit in most places.