(Suggestion) Mob options and skill mechanics related to item frame entities

Item frames are usually useful for making decorations for their ability to contain an item with custom model data, and easier to use comparing with armorstands. So I think it'll be well to add some functions to modify item frames.

Mob options:

1. Item, decides the item containing by the item frame, can be MMOItems;

2. Rotation, the rotation of the item frame;

3. Invisible, makes the item frame invisible;

4. Unbreakable, makes the item frame cannot be taken down by players using left-click;

5. Unchangeable, makes the item into the item frame cannot be taken down or rotated by players.

Skill mechanics:

1. AddItemIntoFrame, adds a specified item into the selected item frames, or changes the item if the targeted item frames are already displaying any item (can be optional by setting skill attributes).

2. RemoveItemFromFrame, removes items from the selected item frames, can be set if drops the item or not;

3. RotateFrame, rotates the selected item frames, can be clockwise or anti-clockwise.