Reduce number of data pulls from Airtable

[cweems]

There are a few instances where the middleware is pulling all contacts from Airtable, just to match a single record. If we can refactor these then we'll be able to reduce the number of API calls to Airtable and improve app load time.

Functions to refactor:

• getCustomerByNumber: called when a new conversation is created by Twilio Conversations on inbound SMS.
• getCustomerById: called when a contact is viewed form the contact list.

We may also be able to filter the list of records retrieved from Airtable by filtering by owner.

• Filter airtable contacts returned by owner in request.