Allow add 1 point hair objects to make them instance base

Newly added hair object is not only useful for hair, but can be a base for instances.

But currently it's a bit tricky to use for the purpose. I suggest these to make them more useful for instances.

1. Allow to add hair object that has only 1 point.
2. Put "scale", "N" (or "tangent") attributes to the 1 point hair objects.
3. Make brush actions modify the attribute instead of shape of the hair, when it is 1 point hair object.
4. Possibly distinctive visualization?

Thanks.