172 validate school fields

the first part of the validation for school fields 
That's a lot of `if/else`. We can simplify this to:
```python
if international == School.LOCATION_INTERNATIONAL:
    if not re.match(...):
        raise serializers.ValidationError(...)
else if not re.match(...):
    raise serializers.ValidationError(...)

return attrs
```

Also, why not make this a function in `validators`? We should be reusing it for `secondary_phone` as well.