should add committee membership data from the new knesset API

### expected outcome
this is only a suggestion, feel free to implement it another way
```
from knesset_data.dataservice.persons import PersonPosition
for person_position in PersonPosition.get_all():
peson_position.PersonID
person_position.CommitteeID
# all other fields..

# mk = Member of Knesset
# this method should return the standard member id, like:
# 901 = איציק שמולי
person_position.get_mk_id()

# given person_position.CommitteeId
# fetch and return a dataservice.committees.Committee object
person_position.get_committee()
```

### relevant documentation and details:
* knesset data API documentation - https://docs.google.com/document/d/1FHqabNsYlSNyul1lArmnONLHnYGA4XQNMs3k-dPgUok/edit
* how to add a dataservice object - https://github.com/hasadna/knesset-data-python/tree/master/knesset_data/dataservice#how-to-add-a-new-collection-dataservice
* @davi17g is working on similar issue, have a look at his PR - https://github.com/hasadna/knesset-data-python/pull/8
* related knesset-data issue: https://github.com/hasadna/knesset-data/issues/133