feat(login): move login code into src folder
The de facto standard for component organization is 'src/' for code and 'test/' for tests. Login wasn't following this and has now been updated.
BREAKING CHANGE: If you've required the Login component directly, e.g. require('pubsweet-component-login/LoginContainer'), you have to change those requires to require('pubsweet-component-login') and get Login (LoginContainer) from the export.