Refactor screencontrol to inputmanager

The "screen control" handled user input, which happened to be only
used to control the screen.

The controller and screen were passed to every function. Instead, group
them in a struct input_manager.

The purpose is to add a new shortcut to enable/disable FPS counter. This
feature is not related to "screen control", and will require access to
the "frames" instance.

app/src/inputmanager.h

@@ -0,0 +1,24 @@
+#ifndef INPUTMANAGER_H
+#define INPUTMANAGER_H
+
+#include "common.h"
+#include "controller.h"
+#include "screen.h"
+
+struct input_manager {
+    struct controller *controller;
+    struct screen *screen;
+};
+
+void input_manager_process_text_input(struct input_manager *input_manager,
+                                      const SDL_TextInputEvent *event);
+void input_manager_process_key(struct input_manager *input_manager,
+                               const SDL_KeyboardEvent *event);
+void input_manager_process_mouse_motion(struct input_manager *input_manager,
+                                        const SDL_MouseMotionEvent *event);
+void input_manager_process_mouse_button(struct input_manager *input_manager,
+                                        const SDL_MouseButtonEvent *event);
+void input_manager_process_mouse_wheel(struct input_manager *input_manager,
+                                       const SDL_MouseWheelEvent *event);
+
+#endif