Adding dotkit support to TAU.

- New spack.hooks package
  - contains modules with pre and post install hooks

- New dotkit hook module
  - generates/removes dotkits on install/uninstall

- New spack use, spack unuse commands
  - use same syntax as install/uninstall

- New setup-env.bash script
  - Sets up path, dotkit support

- new spack dotkit command
  - used by script to parse specs, generate
    specs of installed pckages for dotkit file names