Remove (or hide) object type?

Object type isn't seeing any love and, at least in Blaze, I find it useful to interpret numpy dtype `'O'` as `string`. There are trade-offs here. Thought I'd ask for discussion.

@mwiebe thoughts?

The issue names no files, tests, or entry points to inspect. Start by identifying how the object type is represented and used in datashape and how Blaze interprets NumPy dtype 'O'. Done requires a decided direction—remove the type, hide it, or retain it with defined string behavior—plus agreed tests or documentation.

Written by the indexing model from the issue text.