Discuss boss bars

[caojohnny]

Boss bars are currently being implemented by @nickrobson

We need to go over the API and the implementation details here.

Some/several TODO items are found in the linked file:

• https://github.com/TridentSDK/Trident/blob/bbb3b16a2f014880836391504061e9e786e5e6b6/src/main/java/net/tridentsdk/server/ui/bossbar/DefaultBossBar.java