Remove outdated entries from .gitignore
Remove old theme files

The bridgepdx and default themes were extracted to:
https://github.com/osbridge/old-ocw-themes

The Ignite themes, with updates, can be found in the OpenProposals
repository: https://github.com/igal/openproposals/tree/master/themes
Remove the 'public' directory
Remove old .hgignore file
Use git to determine files for gemspec