Move editor_factories from traits into traitsui

Related to https://github.com/enthought/traits/issues/1004

Background:
One of the solutions for fixing https://github.com/enthought/traitsui/issues/790 is to avoid caching editor factory in global states. I think that *is* the correct fix, but since the editor factory lives in `traits`, we ended up working around the issue by copying some of the traits on the factories across onto the editor (see #859). The workaround is less ideal because not only the editor has a reference to the factory object, it has to repeat some of the traits on the factory. (Turns out this workaround breaks other downstream code and so this needs to be fixed again).

Had the editor factories been in the traitsui code base, we would have been able to fix the issue properly in traitsui. The editor factories also result in cycle dependency between traits and traitsui.

This issue is for moving the editor factories to traitsui so that they can be maintained here. This will require concerted effort with releases of traits as well.