Create a method that allows us to add to WELLLIST

[jonnyh404]

Is your feature request related to a problem? Please describe.
Lack the ability to add to a WELLLIST or create a new well list for a given datetime.

Describe the solution you'd like
Use some of the add_operations in the network file to be able to add a Welllist. Will need to make Welllist inherit from DataObjectsMixin.

The required solution will need to take a welllist name, list of wells to be added and result in the following being added to the network file.

model.network.welllists.add(welllist_name='welllist_name', wells=['well1', 'well2'], date='01/01/2020')

TIME 01/01/2020
WELLLIST welllist_name
ADD
well1
well2
ENDWELLLIST

Additional context
This is required to be able to add an RFT at a specified datetime.