Improve installation process and update documentation

Move installation docs to new INSTALL.md
Move contribution section to new CONTRIBUTING.md
Update instructions in application.example.yml
Update instructions in settings.yml
Add new scripts and update old ones to facilitate installation and deployment

Instead of exiting the DB population task, allow all valid entries to go through,
and capture invalid ones in a new file so they can be easily identified and fixed.
Merge pull request #163 from codeforamerica/installation-docs

Improve installation process and update documentation