Add autocomplete attribute to password form fields

Problem/Motivation

Currently Google Chrome produces warning about missing autocomplete on pages with passord input element.

[DOM] Input elements should have autocomplete attributes (suggested: "current-password"): (More info: https://goo.gl/9p2vKq)

Steps to reproduce

Navigate to /user/login page
Open JS console in Google Chrome.

Proposed resolution

Use autocomplete="new-password" for the password input in a login form.
Use autocomplete="current-password" for a password input on register form.