Minor sea chicken improvements

[sprunk]

Chickens were never designed for sea and ultimately these won't change that but they seem like a low mana way to improve the situation:

• give chicken projectiles the ability to pierce water.
• probably make melee chickens walk underwater (because the juicier eco buildings don't float)
• #sonarLives
• there are reports that chickens have some sort of slowdown on water, check whether this is true and remove.

[ArchShaman]

I've got a branch that's working on the issue. Basically I've changed the following:

• Melee units walk underwater. (Taken from the duck unitdef)
• Goo and spores now pierce the water. Spores is a standardization because some spore types cannot pierce the water, but others can.
• All chicken units now have sonar = sight.
• Dodo now walks underwater. (It's a "melee" unit, right?)