Normalize phone numbers

[ghubstan]

Reluctantly added new dependency: 343 kb Google libphonenumber.
See https://github.com/google/libphonenumber

Created new PhoneNumberValidator + Test. Validator hides
no arg constructor; public constructor requires two letter
ISO country code for validating national numbers.

If input passes validation, it is transformed into E.164 format
and cached in a class field, accessible via getter method.
See https://en.wikipedia.org/wiki/E.164

Five new i18n error message properties (validation.phone.*) were
added to the default and Portuguese display string property files.
A native Portuguese speaker should review/change the PT strings.

This is partial fix for Issue #3042 -- validator will be integrated
into the GUI after PR(s) approved / merged.

[battleofwizards]

Thanks, looks promising! Also, very nice you provided the tests.

Short on time / quick and dirty comments:

• have you reviewed dependencies of libphonenumber, if any?
• have you checked the library is self-contained and never calls home?
• can we migrate away from static fields to instance fields? if not, is it verified libphonenumber is fully thread safe?
• validate() is a huge method, would be nice to name its fragments by extracting private methods
• the tests beg for helpers encapsulating the intent, like assertInvalid or whatever is idiomatic for this test framework (refuteValid, assertNotValid?)
• you cannot directly edit translations except English. See https://github.com/bisq-network/bisq/blob/master/docs/translation-process.md for details

[ManfredKarrer]

I am not sure if the use case here is worth the risk of adding a new dependency (even if its a google library). We basically want to go the opposite way to reduce dependencies as far as possible.

[ghubstan]

Closing PR. Will redo w/out another dependency.