Add optional prefix value to plugin.yml. Addresses BUKKIT-838

By: Aidan Matzko <amatzko48@gmail.com>

paper-api/src/main/java/org/bukkit/plugin/PluginDescriptionFile.java

@@ -30,6 +30,7 @@ public final class PluginDescriptionFile {
     private String description = null;
     private List<String> authors = null;
     private String website = null;
+    private String prefix = null;
     private boolean database = false;
     private PluginLoadOrder order = PluginLoadOrder.POSTWORLD;
     private List<Permission> permissions = null;
@@ -159,6 +160,10 @@ public final class PluginDescriptionFile {
     public String getClassLoaderOf() {
         return classLoaderOf;
     }
+    
+    public String getPrefix() {
+        return prefix;
+    }
 
     private void loadMap(Map<?, ?> map) throws InvalidDescriptionException {
         try {
@@ -311,6 +316,9 @@ public final class PluginDescriptionFile {
         } else {
             permissions = ImmutableList.<Permission>of();
         }
+        if (map.containsKey("prefix")) {
+            prefix = map.get("prefix").toString();
+        }
     }
 
     private Map<String, Object> saveMap() {
@@ -348,6 +356,10 @@ public final class PluginDescriptionFile {
         if (classLoaderOf != null) {
             map.put("class-loader-of", classLoaderOf);
         }
+        
+        if (prefix != null) {
+            map.put("prefix", prefix);
+        }
 
         return map;
     }