App susceptible to scrypt DOS via login form

[brassy-endomorph]

Is your feature request related to a problem? Please describe.

The app is susceptible to DOS via scrypt by allowing arbitrary length input on the LoginForm.

hushline/hushline/routes.py

Lines 71 to 73 in 53c65ee

	class LoginForm(FlaskForm):
	username = StringField("Username", validators=[DataRequired()])
	password = PasswordField("Password", validators=[DataRequired()])

Describe the solution you'd like

We should have a limit on that. And since this has potential to lock users out of their accounts if we ever change the password max length, we should have some sort of test to ensure that the limit doesn't tighten if we change the registration password length.