Move releasers to sub-directory.
Move taggers to sub-directory.
Refactor config overriding.

Merge rel-eng/tito.props with package specific tito.props. Package specific
values will be used whenever the same property appears in both.

This patch deprecates the use of [globalconfig], instead favoring
[buildconfig]. Globalconfig will continue to work and just print a warning to
the user, support will be removed entirely later on.
Remove a very old hack for assuming config from Makefiles.

This predates build.py.props which predates tito.props. Extremely unlikely
anyone is still using this.
Remove deprecated support for build.py.props config filename.
Stop writing temp file to load tito.props from past tag.