SEVER-10521 Update write commands types to comform to v0.4 of the spec

This is the first pass on the write protocol changes made for v0.4.
The changes and fixes in here are:

* commands take name of a collection, rather than a namespace
* continueOnError is now called ordered
* w:0 returns a condensed responses in case of errors
* upserted is now only returned in updates
* prep work for returning the _ids of upserted documents (but
  not there yet
* we're reporting (tentatively) error messages in the 'errMsg'
  field (as opposed to the 'errmsg' one). If this causes some
  havoc, we'll stick to the old way and live with one non-stadard
  named field.