add extraction_qti and extraction_time as properties of units

[sanslash332]

Will be interesting add the option to put that parameters to the workers, to give the option to create workers with different extraction possibilities.
Of course, if the parameter is missing, use the extraction qti and time defined in the resource.

example:

def super_peasand
is_a peasand
extraction_qti 3 3
extraction_time 1 2

the arguments is an array. one value per defined resource.