Loosen restrictions on phone numbers

[xuset]

Phone numbers sent to the api that contain spaces and normal punctuation like dashes or paranthesis should be acceptable. The api should transform these phone numbers by stripping all non-numeric characters (except for the optionally prepended "+"). No assumptions should be made on the expected number of digits in a phone number.

[georgeaf99]

Furthermore, we should be using the Googles phone validation library (https://github.com/daviddrysdale/python-phonenumbers) to validate all phone numbers before they are accepted by the API.

@xuset do you think we can implement this at the model layer?