Allow users to create Tools

:construction: :rotating_light: :construction_worker: :rotating_light: :construction:

This is current in progress, and it is kind of a beefy PR.

This introduces the `Tool`, a way for folks to share their various tools and plugins on Supermarket.

Trello card: https://trello.com/c/oV2dAj7h

The todos lives in the Trello card. :smile_cat: 
Not sure if the intention here is to test that the user is directed to the `tool.user` profile path or just the current user (I know that they're always the same user) but you could probably save a little time in the database if you just did something like this

```ruby
let(:user) { create(:user) }
before { sign_in(user) }

# later on

expect(response).to redirect_to(tools_user_path(user))
```

Just a suggestion I'm not sure if showing that it's redirected to the `tool.user` is important or not.