Implement Common Item Functionality

[mwerezak]

GUI Items

• [x] get_all_items
• [x] does_item_exist
• [x] delete_item

Configuration

• [x] configure_item
• [x] get_item_configuration

Values

• [x] add_value
• [x] get_value
• [x] set_value
• [ ] incref_value
• [ ] decref_value

Callbacks

• [x] get_item_callback
• [x] get_item_callback_data
• [x] set_item_callback
• [x] set_item_callback_data

Containers

• [x] is_item_container
• [x] get_item_parent
• [x] get_item_children

Other Properties

• [x] get_item_rect_max
• [x] get_item_rect_min
• [x] get_item_rect_size
• [x] is_item_activated
• [x] is_item_active
• [x] is_item_clicked
• [x] is_item_deactivated
• [x] is_item_deactivated_after_edit
• [x] is_item_edited
• [x] is_item_focused
• [x] is_item_hovered
• [ ] is_item_shown just gets the 'show' config, which is already implemented
• [ ] is_item_toggled_open to be added only on widgets that need it
• [x] is_item_visible

Placement

• [x] move_item
• [x] move_item_down
• [x] move_item_up

[mwerezak]

Style and color overrides for individual widgets moved to #13

[mwerezak]

More or less complete!