With this commit the WellsManager will check the status of completions
before adding them to the internal struct wells
datastructure. Completions can be in the four states:
OPEN, SHUT, AUTO, POPN
Completions with state == SHUT will be ignored, wheras the wellsmanager
will throw if the states AUTO or POPN are encountered. The WELOPEN
keyword can also have the value 'STOP'; for completions that is
translated to 'SHUT' by Schedule object.