Reorganized file structure

Added collects dir which mirrors possible future install of the
sicp languages as a racket collection. Moved files into sicp/
subdirectory of that collects dir (collection will be called "sicp").

Moved bar.scm test file into top-level directory.
Added gitignore
Organized ch1 language files

Files all import and reference each other correctly. Actual implementation
needs lots of work.
Added official SICP solution code