Unify Options and FirstRun Pages from Chrome Extension

This pull request adds a build option, specified as `python build.py --platform=chrome`, that will build the Chrome extension's options and FirstRun pages into the Privly-applications bundle. This solves an issue where the user can't find the extension-specific options without going into Chrome's extension options. If you build the applications without the option it will not build the platform-specific apps or integrate them into the navigation. When I merge this PR, I'll build the apps for chrome in a separate branch and re-target the Chrome extension's submodule at the relevant commit.

See: Pull request https://github.com/privly/privly-applications/pull/71 for just the templating changes sans the Chrome-specific changes.