Add the life label on top of the game

This patch only prints the life of the player. The logic of game over
will be added to the game in future releases.
Anchor the HUD elements on the screen

Fix the HUD on the screen, so that when the player moves in
the map, the HUD doesn't desappear.
Add drop bar

Add a sprite sheet for the drop bar and methods for increase and decrease
the drop bar when the player gets a new drop.