Some minor changes in readme file
First shot with changing header. Added separate buttons for session. Removed divs used to change theme and added one buton instead
Added actions to theme switch button
Added light and dark styles to buttons located in header
Added titles to header's buttons
Added possibility to sign into last.fm account
Added full session handling. It can be created and closed using buttons located in page's header
Added missing semicolon
Added hover styles to header's buttons. Aslo removed unneccesary styles from css files