Add ability to do things upon button/cube/platform press

[LukeSaward]

Currently, the Component struct contains an event for detecting change in the level, but not in cubes, platforms and buttons.

With this added, the struct would look as follows:

struct Component {
    id: int,
    conflicts_with: List<int>,
    draw_hud_text: fn(string) -> string,
    draw_hud_always: fn(),
    tick_mode: TickMode,
    // largest delta time wins and is used for the next frame
    requested_delta_time: Option<float>,
    on_tick: fn(),
    on_yield: fn(),
    on_new_game: fn(),
    on_level_change: fn(int, int),
    on_buttons_change: fn(int, int),
    on_cubes_change: fn(int, int),
    on_platforms_change: fn(int, int),
    on_reset: fn(int, int),
    on_element_pressed: fn(ElementIndex),
    on_element_released: fn(ElementIndex),
    on_key_down: fn(KeyCode, bool),
    /// triggered even when in the menu
    on_key_down_always: fn(KeyCode, bool),
    on_key_up: fn(KeyCode),
    /// triggered even when in the menu
    on_key_up_always: fn(KeyCode),
    on_mouse_move: fn(int, int),
    on_component_enter: fn(),
    on_component_exit: fn(),
    on_resolution_change: fn(),
    on_menu_open: fn(),
}