Remove storing of password in browser

Plaintext password was stored in localStorage. This was removed and replaced
by token.
Username is still stored -- we display it in the navigation bar.
Tests were updated to use only the token and a check for username in navbar
was added.

Implements: blueprint access-control-master-node-improvments
(cherry picked from commit c1ee8dfede79b354601f389a91a7244a2920945a)

Conflicts:
	nailgun/static/js/app.js
	nailgun/static/js/views/dialogs.jsx
	nailgun/static/js/views/layout.jsx
	nailgun/static/js/views/login_page.jsx

Change-Id: Id9a053e119f6826eda5472629f7d09e618297403
Merge "Remove storing of password in browser" into stable/5.1