institutions and harvest feeds

Institutions and harvest feeds (user-entered data meant primarily for human consumption)
 - basic models, controllers, views, routes, and migrations
 - rake tasks to save and delete sample institution and harvest feed

For reference, the ER diagram is here: https://docs.google.com/a/dp.la/drawings/d/1Wmtq6x_VBjJGgwAMhT2qUHvkuQAygMLooXd0K2eOAPo/edit

You can test in your browser by following the README instructions to generate and start a dummy application, and then creating a sample institution.  Go to `http://localhost:3000/krikri/institutions`.  You should see one institution listed.  A link from that page should take you to a view with data for that institution.  From there, another link should take you to a view with data for one sample harvest feed.

Once @mb has customized the user model, we can integrate it with the institution model and possibly rethink the routes to fit with admin and general user dashboards.
Database cleaner did not fix the problem, but it did streamline testing in other ways, so I added it with this commit: https://github.com/dpla/KriKri/commit/db8e010d7b0a419023ae387844bd4219e7c75744