git-codereview: rename from 'git-review' to 'git-codereview'

Mostly trivial search and replace, except for hooks.go which
includes a special case to remove the old git-review hooks.

Change-Id: Ic0792bb3e26607e5e0ead88958e46c3ac08288cd
Reviewed-on: https://go-review.googlesource.com/1741
Reviewed-by: Russ Cox <rsc@golang.org>