Install minitest and Capybara

Also, update other gems and clean up Gemfile.
Change minimum password length
Create a basic test for managing galleries
Use Selenium with Capybara

And update the basic test. It seems to work better now. Wish I could
figure out the database madness.
Use Capybara assertions

Failure messages are much more descriptive.
Add simple tests for Categories

There’s a little bit more to test than with Galleries. The core
functionality should be well covered.
Fix the environment setting on Minitest

It now uses the test database. Still no luck getting database_cleaner
to work. The tests run very smoothly, though.