Revert "Delete HotkeyRegistration.java"

This reverts commit df676635

src/model/HotkeyRegistration.java

+package model;
+
+public interface HotkeyRegistration {
+    /**
+     * Registers a given hotkey.
+     * @param hotkey The hotkey to be registered. Must contain a unique ID.
+     * @return If the registration was successful.
+     */
+    boolean registerHotkey(Hotkey hotkey);
+
+    /**
+     * Unregisters a hotkey with the given id.
+     * @param id The id of the hotkey to be unregistered.
+     * @return If the unregistration was successful.
+     */
+    boolean unregisterHotkey(int id);
+}