Convert to a bashrc.d type system.

Debian systemd have a ~/.bashrc.d that lets the  system install scripts
for a user.  It's nice and flexible, so this models after that.

Add a bashrc.d/actions/, bashrc.d/env/, bashrc.d/flavor/, and
bashrc.d/local/ to the scripts repo.

During setup, bashrc.d/local is copied to $HOME/.bashrc.d/.

Login happens like this:

- First, bashrc.d/env/* is sourced, to set up the base environment.
  - This includes setting the flavor of linux
- Next ${HOME}/.bashrc.d/ is sourced to override the env locally.
- Next bashrc.d/actions/* is sourced, to set common aliases/commands
- Finally, bashrc.d/flavor/$FLAVOR/* is sourced to set up for the
  flavor.