N-Gons Primitive: Added new parameters to create n-gons

[micheus]

The new parameters allow we set different ways to construct the object computing it by
Radius(current one), Apothem and Segment length.

This can give us more precision for some shapes.

[ivla]

Unfortunately it cannot make N-gon with more than 20 edges.
And I think that there's no need to use a sliders - numeric input field is enough.
(wings3d v2.4.1 + patch from here)

Is it possible to correct this?

[micheus]

Yeah. You are right about 20 be a lower value.

I had already increased it for the PR, but I forget to update the file - I made it now.

The value was increased to 100, since using a higher value doesn’t seem to make sense; otherwise, a cylinder might work fine.

The use of a slider indicates that the value represents a range.