More types of cell lines.

[Ad115]

The current implementation of Cell and CellLine doesn't allow easy creation of different cell types that can perform different actions, besides, the actions that a cell can perform are not easily customizable.

This problem may be solved by implementing a mechanism for editing cell's actions at runtime, maybe something like:

def division_fn(cell, *args, **kwargs):
    "The cell division action."
    # Let there divide...

cell.add_action( {"division": division_fn} )

Although it is not really clear how the logging mechanism may be affected by this.