[reSIProcate] [reTurn][patch][gsoc] Added support for multiple users

[Catalin Usurelu <catalin.usurelu5@xxxxxxxxx>]

The current implementation of reTurnServer supports a single
username/password.  These values are specified in /etc/reTurnServer.config.

I've added support for multiple usernames and passwords.

Parameter in the main config file, for database file:

UserDatabaseFile = /etc/reTurn/users.txt

Format of each line: login:password:realm:state

Attachment: reTurn_multiple_users_database.patch
Description: Binary data