[B+C] Add broadcast function that sends to a player list

**The Issue:**
Currently, the only way that you can send a message to a select group of players is with your own for loop or permissions, which can be redundant at times.

**Justification of this PR:**
This PR includes a method for broadcasting a message to a list of players, which is included in the Bukkit.java and Server.java classes.

**PR Breakdown:**
This PR adds one new method to the Bukkit.java and Server.java classes,
```java
ArrayList<Player> players = new ArrayList<>();
players.add(Bukkit.getServer().getPlayer("KeybordPiano459"));
Bukkit.broadcast("Hello world!", players);
```

**Testing Material and Results:**
I created some sample code on how you would use this method here:
https://gist.github.com/keybordpiano459/7b77760f74b39aeb8006

**Relevant PR(s):**
https://github.com/Bukkit/Bukkit/pull/818

**JIRA Ticket:**
https://bukkit.atlassian.net/browse/BUKKIT-3857