First fixes and improvements

So many hours after the deadline of the jam, here are some fixes and improvements:

• now on same waves there is a chance for weaker monsters to be spawned, as intended;
• fine-tuned the waves to be easier in order to make them beatable;
• added sound effects and music;
• the floating texts are a bit better;
• there is fullscreen text just for the upgrades and weapon drop announcements;
• gui information text style update - now it drops shadow as the floating texts;
• now the bomb actually explodes when "planted" near the sink;
• bullet hit animation;
• fine tuned some weapons and monsters;
• a lot of playtesting.

I feel like the game is a bit dull. There must be a lot of more action. Now you just stand at a position and shoot. Also, I might create something like a portal to wrap you near the fridge after the wave ends, because I find walking forward and backward sooo annoying.