Moving walls

[grmpyktn11]

This is a Node which uses Path2d and a collisionShape (from staticbody2d)

• It uses a export variable to progress the object along the path
• There is a bouncing exported variable which allows walls to move just once or not
• The path is editable if you check Editable Children fixes #88

[Justin1L8]

very similar functionality already implemented for #87. closing this issue without merging.