Despite myLayouts currently being more popular in examples, make
them all myLayout as in man/xmonad.hs to avoid mixing them in the
same module as was done a few places, leading to confusion for some users.
The Replace and Merge messages are added to support layouts sending a list of
windows that should be skipped over. The sources are tagged by a string key, so
it is possible though unlikely for different sources of boring windows to
interfere with eachother.
