Move KuitSetup code over into files matching its name
9ea3a10b (pre-KF5.0) only added a redirecting header to have some CamelCase include matching the main class name, but kept the old header and source file names around, even when there was no more class of the name.
Old header now instead redirects to new header, instead of the other way around. And deprecating the old includes will allow to remove the old headers for KF6.