Support multiple TURN and STUN servers

In #5 (closed) support is being added for one TURN / STUN server, at some poing in the future this should be expanded to multiple servers, this is the default /usr/share/bbb-web/WEB-INF/classes/spring/turn-stun-servers.xml configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!--

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Copyright (c) 2012 BigBlueButton Inc. and by respective authors (see below).

This program is free software; you can redistribute it and/or modify it under the
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-->
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
            ">

    <bean id="stun1" class="org.bigbluebutton.web.services.turn.StunServer">
        <constructor-arg index="0" value="stun:stun.freeswitch.org"/>
    </bean>

    <!--bean id="stun2" class="org.bigbluebutton.web.services.turn.StunServer">
        <constructor-arg index="0" value="stun:stun2.example.com"/>
    </bean-->

    <!--bean id="iceCandidate1" class="org.bigbluebutton.web.services.turn.RemoteIceCandidate">
        <constructor-arg index="0" value="192.168.0.1"/>
    </bean-->

    <!-- Turn servers are configured with a secret that's compatible with
         http://tools.ietf.org/html/draft-uberti-behave-turn-rest-00
         as supported by the coturn and rfc5766-turn-server turn servers -->

    <!--bean id="turn1" class="org.bigbluebutton.web.services.turn.TurnServer">
        Secret:
        <constructor-arg index="0" value="secret"/>
        TURN server URL, use turn: or turns:
        <constructor-arg index="1" value="turn:turn1.example.com"/>
        TTL in seconds for shared secret
        <constructor-arg index="2" value="86400"/>
    </bean-->

    <!--bean id="turn2" class="org.bigbluebutton.web.services.turn.TurnServer">
        <constructor-arg index="0" value="secret"/>
        <constructor-arg index="1" value="turns:turn2.example.com:443"/>
        <constructor-arg index="2" value="86400"/>
    </bean-->

    <bean id="stunTurnService" class="org.bigbluebutton.web.services.turn.StunTurnService">
        <property name="stunServers">
            <set>
                <ref bean="stun1" />
                <!--ref bean="stun2" /-->
            </set>
        </property>
        <property name="turnServers">
            <set>
                <!--ref bean="turn1" /-->
                <!--ref bean="turn2" /-->
            </set>
        </property>
        <property name="remoteIceCandidates">
            <set>
                <!--ref bean="iceCandidate1" /-->
                <!--ref bean="iceCandidate2" /-->
            </set>
        </property>
    </bean>
</beans>