Make use of django_main for password_reset templates

Remove duplicated code and make sure those views use the same visual
identity.
Update password reset views style

Reuse the style from login and register views.
Remove all the specific style.
Fix 'change my password' button font size
Merge pull request #4145 from IONISx/tusbar/rewrite-password-reset-templates

Make use of django_main for password_reset templates