remove stats system

improve operations and make them extendable more easily and let other plugins add operations, like requirements 
move requirements/operations out of ranks class as they will be used in prestiges

src/main/java/sh/okx/rankup/requirements/Requirement.java

@@ -0,0 +1,63 @@
+package sh.okx.rankup.requirements;
+
+import lombok.Getter;
+import org.bukkit.entity.Player;
+import sh.okx.rankup.Rankup;
+
+public abstract class Requirement implements Cloneable {
+  protected Rankup plugin;
+  @Getter
+  protected String name;
+  private String value;
+
+  public Requirement(Rankup plugin, String name) {
+    this.plugin = plugin;
+    this.name = name;
+  }
+
+  protected Requirement(Requirement clone) {
+    if (clone != null) {
+      this.plugin = clone.plugin;
+      this.name = clone.name;
+      this.value = clone.value;
+    }
+  }
+
+  public void setValue(String value) {
+    this.value = value;
+  }
+
+  public String getValueString() {
+    return value;
+  }
+
+  public double getValueDouble() {
+    return Double.parseDouble(value);
+  }
+
+  public int getValueInt() {
+    return Integer.parseInt(value);
+  }
+
+
+  /**
+   * Check if a player meets this requirement
+   *
+   * @param player the player to check
+   * @return true if they meet the requirement, false otherwise
+   */
+  public abstract boolean check(Player player);
+
+  /**
+   * Get the remaining amount needed for <code>Requirement#check(Player)</code> to yield true.
+   * This is not required and is only used in placeholders.
+   *
+   * @param player the player to find the remaining amount of
+   * @return the remaining amount needed. Should be non-negative.
+   */
+  public double getRemaining(Player player) {
+    return getValueDouble();
+  }
+
+  public abstract Requirement clone();
+}