Pass CommandContext to commands

CommandContext is the carrier of dependencies.
Currently, it only carries a DropProvider, but
it will grow bit by bit as more static singletons
and other similar structures get refactored.

src/main/java/client/command/commands/gm0/ToggleExpCommand.java

@@ -25,6 +25,7 @@ package client.command.commands.gm0;
 
 import client.Client;
 import client.command.Command;
+import client.command.CommandContext;
 
 public class ToggleExpCommand extends Command {
     {
@@ -32,7 +33,7 @@ public class ToggleExpCommand extends Command {
     }
 
     @Override
-    public void execute(Client c, String[] params) {
+    public void execute(Client c, String[] params, CommandContext ctx) {
         if (c.tryacquireClient()) {
             try {
                 c.getPlayer().toggleExpGain();  // Vcoc's idea