Decimate Convex and concave options

Convex geometry tends to have more of an impact on silhouette and so I think when making LODs or optimizing geometry, that it would be beneficial to have more control over this in the decimation modifier.

I suggest specifically for the Planar option on the decimate modifier and possibly for collapse option, that an angle limit can be set for concave or convex geometry. I see it as a check box to activate convex or concave and then turns on an angle slider, or possibly better, a slide that initializes after being changed to a non zero number.