Use Waterfall's methods to add and remove servers

[Sneakometer]

Related to PaperMC/Waterfall#645
So basically there is a slim chance breaking the TMap in the Configuration class of Waterfall everytime a server is added/removed at the same time another thread is accessing it. Waterfall intruduced a lock object aswell as dedicated addServer() and removeServer() methods to mitigate this issue. I request CloudNet to use these methods, if they are found, or else fall back using the map to still keep the BungeeCord compatibility.

Reasons for inclusion into the CloudNet code base:

• Fix synchronization issues accessing the server list
• Possibly fix java.lang.NullPointerException in BungeeCord #482
• Keep BungeeCord compatibility
• Janmm14 suggested this

Planned audience:

• All Cloudnet + Waterfall users

Preview of pseudo code :

• Check if addServer() and removeServer() methods are present using reflections
• If yes, use them to add and remove Servers in the Bridge Module
• If no, just do it the old way

[derklaro]

Implemented in branch better-service-to-proxy-register please test and give feedback :) Thank you

[Sneakometer]

Now running 1 week in production without any issues. I think it's safe to merge.

[derklaro]

Was implemented in 86c49a5 and will be available in the next release. Thank you for your report :)