Password match fix and improvement

[dgvirtual]

• Fix password match on register view
• add debounce
• add two-way checking (checks not only on typing in check_password but also when typing in password field)
• improve placement and visibility of password-match indicator
• add preview password functionality in login and register screens; if password is revealed by user, remove requirement to type it second time
• use font-awesome for show/hide password and password match/mismatch indicators