Switch to a sqlite backing store

@andymoe pointed out that it was a little silly to use an XML
backing store. I wonder why this is the default when you add
core data to a project in xcode 4 for an OS X project.
Rename TwIRCk to twIRCk

Well, start to at least. The chatview window is still capitalized,
but this is a step in the right direction.
Rename menu items

Also removed Recent Servers since I don't think I'll be implementing
that before a release.