Let Displace modifier use any transform orientation

The Displace modifier currently offers several Directions, but they do not cover all use cases. Allowing it to use any transform orientation will give people more options (local, normal, etc.) For each, it should be possible to use X, Y or Z, or use a texture or vertex paint's RGB to control them.

Additionally, it would be nice to be able to control displacements with vertex group weights. Currently the influence of the texture can be limited to only affect a certain group. It would be useful to also have an option to define the displace amount based on a vertex group, instead of only a texture. The midlevel field would also need to apply to this vertex group.

This would allow the displacement modifier to be used for almost any translation you can normally do in edit mode, and would not require the clutter of painted textures when often a vertex group is enough.