Don't use post.php for CPT editing

[boonebgorges]

I realize that the default post.php interface was the fastest way to build the first version of this plugin, but I don't think it's good for the long term. A few reasons:

1. Incompatibility with multisite. See Network Admin compatibility #3.
2. We don't (and won't) use most of what post.php offers: the rich text editor, autosave.
3. The language and interface in the Publish metabox doesn't make a lot of sense for Types.

I suggest we build our own. I have a couple ideas for what it might look like. I'll try to wireframe something in the upcoming weeks.