Modify health bar and lightly modify the health HUD code.

[Rohesie]

Kept the base code the same but modified the following:

• When at 100% (full health) or -100% (dead) the health bar is invisible. The health icon already informs if the person is dead or alive, so we diminish visual pollution here.
• The health bar updates in 10% health intervals from 100% to 50% health, and in 5% ones from 50% to 0%, to add granularity to low-health statuses, which are more important.
• The health bar blinks slowly when under 5% health, faster when under 0% health, and even faster when under -50% health (crit range).

[ninjanomnom]

I'd like this whole switch to get replaced with a single formula at some point and just have a state every 5 steps but this is fine for now.