Post Jam update

Not a huge update yet but tried to work on issues reported by voters of Jam.

Here are the following changes
- made enemies a bit stronger and gave them some abilities
- added 4th option in hero selection: none - all hearoes will fight by themselves
- added some particle effects to the game.
- enemy center circle now works as their health bar
- damage and heal numbers now show on screen
- found and fixed a bug with warrior where his single attack could hit enemy twice.
- tweeked warrior and ranger AI to stay on one target for at least 1 full second before wanting to switch
- made healers orb slower