Entities that are "planted" on bodies of water are floating.
This does away with the "floating" mode.
To mark that entities should by default be floating when placed in
water the boolean property "floats" has been added.
Through the "water_body" property. An entity which has this is a water
body. If there's a bbox the entity is a lake (bounded), otherwise it's
an ocean (infinite bounds).
An entity becomes "submerged" when it moves into a body of water.
Currently we only check if its y-position is below 0, but we aim to
provide better support for various water entities in the future.
This property tells how the entity should behave when put into
different modes. Currently we only allow for specific transformations
to occur.
The mode specifications are registed in properties where "mode-" forms
a prefix, and the mode a suffix. For example, "mode-planted".
This also does away with the "plantable" property.
