Open-event-server: Refactoring models using helpers from app/helpers

[poush]

I'm submitting a ... (check one with "x")

• [x] refactor request

Currently, this is the usage of helpers in models from app/helpers

projects/open_source/open-event-orga-server/app/models/event.py:
```
7 from sqlalchemy import event
8
9: from app.helpers.date_formatter import DateFormatter
10: from app.helpers.helpers import get_count
11: from app.helpers.versioning import clean_up_string, clean_html
12 from app.models.email_notification import EmailNotification
13 from app.models.user import ATTENDEE

projects/open_source/open-event-orga-server/app/models/event_invoice.py:

3  from datetime import datetime
4  
5: from app.helpers.helpers import get_count
6  from app.models import db
7

projects/open_source/open-event-orga-server/app/models/session.py:

1  import datetime
2  
3: from app.helpers.date_formatter import DateFormatter
4: from app.helpers.versioning import clean_up_string, clean_html
5  from app.models import db
6

projects/open_source/open-event-orga-server/app/models/speaker.py:

1: from app.helpers.versioning import clean_up_string, clean_html
2  from app.models import db
3: from app.helpers.helpers import ensure_social_link

projects/open_source/open-event-orga-server/app/models/sponsor.py:

1: from app.helpers.versioning import clean_up_string, clean_html
2  from app.models import db
3

projects/open_source/open-event-orga-server/app/models/ticket.py:

73 Else False.
74 """
75: from app.helpers.helpers import get_count
76 orders = Order.id.in_(OrderTicket.query.with_entities(OrderTicket.order_id).filter_by(ticket_id=self.id).all())

77 count = get_count(Order.query.filter(orders).filter(Order.status != 'deleted'))

projects/open_source/open-event-orga-server/app/models/user.py:

8  from flask.ext.scrypt import generate_password_hash, generate_random_salt
9  from sqlalchemy.ext.hybrid import hybrid_property

10: from app.helpers.helpers import get_count
11 from app.models.session import Session
12 from app.models.speaker import Speaker
..
20 from app.models.users_events_role import UsersEventsRoles as UER
21 from app.models.panel_permission import PanelPermission
22: from app.helpers.versioning import clean_up_string, clean_html
23
24 # System-wide
```

Since, we are working on removing the app/helpers. We need to work on refactor those models and use helper from app/api/helpers

@niranjan94 @SaptakS Please confirm.

[niranjan94]

Lets move the current helpers directory to vintage folder and start a fresh helpers directory with only stuff that we need.

[niranjan94]

@fossasia/open-event-server-devs please note 👆

[poush]

Work is done, need some reviews and PR will be merged.