Add support for stopped wells

With this PR the simulator distinguish between OPEN, STOP and SHUT wells. 
STOP: Well stopped off above the formation. The total rate is set to zero.  I.e. It allows for flow in the well.
SHUT: Well completely isolated from the formation. The well is removed
from the well list. 

This PR also contain a test case that check that the well rate is zero.

This is the last peace that is needed in order to run the full Norne deck. The results do not match satisfactory yet. 

I do not really understand the sentence (also a minor typo: control), it would be better to same that STOPed wells are kept in the well list but marked as stopped or something similar.