[IDEA] Update many-to-many relationship in models.py

[shi-jie-samuel-tan]

Is your feature request related to a problem? Please describe.
Current many-to-many relationships in our models are duplicated in Django default tables and self-described tables. This could potentially lead to unexpected behavior when linking between models

Describe the solution you'd like
The self-described tables will be removed and all many-to-many relationships will be handled by Django by default

[jkdru]

Does this mean we should comment out the 6 Lookup_ classes at the very end of models.py? (per your text explaining "Django has a default many to many table" so we want to cut out the redundancy of creating extra many to many tables)

What data type should the site_id field in each table become? Currently those are:
site_id = models.ManyToManyField('Sites_all', through = 'Lookup_...')
And the def str(self): for each Siterecs_ class invokes site_id.

Also, should CSVs for loading change the data already listed manually in any of these columns:

• id_ for sites_all table (6 cols here that reference the oid from the other tables)
• site_id for each siterec table (example
  I've never understood how my matching these up in advance works together with the Lookup_ ManyToMany setup, or whether they're ignoring each other.