add sqlite3 module in buildozer build and *.db files
add new color constants
Highscores Screen displays top 10 highscores
Merge branch 'game_board_dev'
fix create highscores table script
update upper layout of GameScreen
update timer color
update Score - on empty chain, don't add any points
display Score on GameScreen
create reset methods for Score and Level classes
Roboto-Medium font
display Level on GameScreen
implement penalties - decrement one second from the timer
prolong timer time
add helper methods to LetterChain: empty and last
reset the timer when the chain is correct and complete