Implement plants

[aenemenate]

Plants will be blocks that are called upon to grow at certain periods.

When called upon, plants which are fully grown will sprout seeds that will go to a random tile. If that tile is occupied by a plant, the seed will die. Plants which are still growing will advance to their next growth stage.

The period will be defined by grass, which grows fastest. The periodic length is once every 4 hours.

grass => GrowthRate = 1

dandelion => GrowthRate = 3

bush => GrowthRate = 5

etc.

Every plant will have a certain number of growth stages which each have an associated graphic. Every plant will start as a colored dot.

Plants will load from xml like everything else.

[aenemenate]

Plants still need to be polled to grow in-game