Modified Swim Ability for Mod support

can now have a swim speed (float) and land speed (float)
as well as floating on the spot whilst in water.

Also tweaked air bubble render to show in exact position of vanilla
render, hid full air meter whilst in water for water breathers.
added depth maintain boolean

some mobs use AbilitySwim just for water breathing, i forgot this...
Also updated Squid's pars
Add & Mapped 2 new abilities

Wither Resistance and Step.
Merge pull request #221 from okushama/master

Modified Swim Ability for better Mod support, added 2 more abilities (Step and Wither resistance)