fix application of color setting, refs #22
fix #21 by ripping not relying on sbt global state any more

Instead, we now have one global singleton which manages the global state.

The change was needed because of sbt/sbt#804 which is now fixed but without a
a backport to all the supported versions if sbt-revolver.
create logging message thunk eagerly when creating shutdownHook to avoid leaking processes

That can happen during development of the plugin when using `publish-local`
is pulling the rug from another running sbt session which is then missing
the thunk when trying to run the shutdown hook.
automatically unregisterAppProcess when it is finished
actually unregister AppProcess after stopping it
fix #25: take colors from global state pool
new settings `reLogTag` to customize log tag shown in front of log messages, fix #23
fix color scheme name, `NoColors` -> `noColors`
bump version