Ensure country code is added to phone number

[tastrax]

It would be useful to validate if the phone number has the country code before submitting to OSM. There is a worldwide push to get numbers corrected. https://maproulette.org/browse/challenges?query=phone

[le-jun]

As long as the number isn’t added as it is into OSM but only creates a note I classify this issue as minor. On the other hand while the "phoneplaceholder" do a pretty good job at hinting the country code I agree that a validation may be necessary. A simple way to do that would be to verify if a + sign is added in the form as there’s a low chance of misstyping it.

[iandees]

I could see us using something like libphonenumber.js to format the number properly as it goes to OSM as a note. That'd be a useful pull request to add.