Start refactoring of command handling (work in progress)

Preparation:
- Remove unused API
- Move some logic from "data classes" elsewhere

src/main/java/fr/xephi/authme/command/CommandUtils.java

@@ -0,0 +1,21 @@
+package fr.xephi.authme.command;
+
+public final class CommandUtils {
+
+    public static int getMinNumberOfArguments(CommandDescription command) {
+        int mandatoryArguments = 0;
+        for (CommandArgumentDescription argument : command.getArguments()) {
+            if (!argument.isOptional()) {
+                ++mandatoryArguments;
+            }
+        }
+        return mandatoryArguments;
+    }
+
+    public static int getMaxNumberOfArguments(CommandDescription command) {
+        return command.hasMaximumArguments()
+            ? command.getArguments().size()
+            : -1;
+    }
+
+}