Use vendored resources, improve test coverage

This PR does the following:

- Allows Omnibus to fetch local files (inside the gem) instead of requiring they exist inside the project
- Prefers local project files
- Adds flags to the generators to allow generating dmg, pkg, and msi assets
- Disables generating dmg, pkg, and msi assets by default
- Adds unity-functional tests for many of the packagers
- Removes `Project#files_path` in favor of `Project#resources_path`
- Standardizes on the term "resource" to refer to a template, asset, or image in a package

/cc @opscode/release-engineers 

@scotthain this does **not** fix your AIX issues, but it gets us much closer. Once we get this merged in, I can start working on refactoring the BFF packager to use this new format and add test coverage.
From looking at existing packages, these expressions aren't matching the directories they are intended to prune.  They should be `**/.git*` and `**/bundler/git`.