Support forward slashes in GameObject names

[sabresaurus]

Right now TransformHelper.GetFromPath() and SelectionManager.GetPath() use forward slashes as a separator between parts of a hierarchy path.

The forward slashes in names should be escaped. The escaping system could use Regex.Split() instead of string.Split(). This is likely more complicated by the fact that GetFromPath() uses transform.Find() which may not support having slashes in object names even with escaping.