Add MIXRegistry, Limber MIX Mock Server and MIX Example

[tarun018]

Standard output shows:

Connecting...Connected Request list of channels. List of rooms at example.tg 1. coven - [email protected]

Request supported nodes for MIX channel: [email protected] Nodes supported by channel [email protected] 1. urn:xmpp:mix:nodes:participants 2. urn:xmpp:mix:nodes:messages 3. urn:xmpp:mix:nodes:presence 4. urn:xmpp:mix:nodes:jidmap

Successfully joined channel [email protected] [warning] Swiften/MIX/MIXRegistry.cpp:24 joinChannel: Channel already joined: [email protected] Successfully left channel [email protected]

Warning is intentional to notify about asking to join an already joined channel.

[tarun018]

Updated based on feedback and added roster sync between clients:

Example (Client 1) :

./Swiften/Examples/MIXListAndJoin/MIXListAndJoin [email protected]/some mixtest2 example.com
Connecting...Connected
Request list of channels.
List of rooms at example.com
	1. coven - [email protected]

Request supported nodes for MIX channel: [email protected]
Nodes supported by channel [email protected]
	1. urn:xmpp:mix:nodes:participants
	2. urn:xmpp:mix:nodes:messages
	3. urn:xmpp:mix:nodes:presence
	4. urn:xmpp:mix:nodes:jidmap

Already Joined channels: 
No channels already joined.

Successfully joined channel [email protected]
[warning] Swiften/MIX/MIXRegistry.cpp:40 joinChannel: Channel already joined: [email protected]

However (client 2 of the same user):

./Swiften/Examples/MIXListAndJoin/MIXListAndJoin [email protected]/someelse mixtest2 example.com
Connecting...Connected
Request list of channels.
List of rooms at example.com
	1. coven - [email protected]

Request supported nodes for MIX channel: [email protected]
Nodes supported by channel [email protected]
	1. urn:xmpp:mix:nodes:participants
	2. urn:xmpp:mix:nodes:messages
	3. urn:xmpp:mix:nodes:presence
	4. urn:xmpp:mix:nodes:jidmap

Already Joined channels: 
	1. coven - [email protected]

[warning] Swiften/MIX/MIXRegistry.cpp:40 joinChannel: Channel already joined: [email protected]

[tarun018]

Updated based on feedback.

[tfar]

@Kev, both @intosi and I have reviewed this PR. If you can give it a review too I can go on and submit it to master.