2020-05-13 updates

- changed movement of base enemies to move only along y-axis as in original Bona

- fix after game over some objects weren't released from memory

 - bonuses add hp/add dmg/add crit rate

- balanced enemies a little bit

- balanced speed of movements

to be added:

- critical rate dmg

- finish bonuses with labels informing of specific bonus

- bona + swarm fighters

- another levels