Add polygon & rectangle drawer

[easytarget2000]

Implement the ability to draw polygons with 3 to 8 edges. The position of the polygons should be given from the centre of the shape. The position the shape should be given on a pixel scale and a grid scale.
Example: A typical grid size is 8. In this case, a 1000x1000px image will be divided into a grid of 8x8. One unit of this grid will be 125x125px large. The polygon drawer can then be told to draw a polygon that is 4 grid units wide at the grid position 3,4. This polygon will be 500px in diameter and centred around the point 375, 500.

TBD: The relationship between diameter and the actual polygon side lengths.

Goals:
http://ginva.com/2016/10/material-design-wallpapers/
https://s1.funon.cc/img/thumb/201809/12/5b999b9fc44d0.jpg
https://s1.funon.cc/img/thumb/201809/12/5b999b9fc44d0.jpg