Add common validators library for input sanitization

[sp3nx0r]

We might want to standardize on common validations that occur often in services, building something similar to Django's validation utility library (https://docs.djangoproject.com/en/3.0/ref/validators/), rather than services glomming in other libraries that we may/may not like. Recent questions from devs I've seen include:

• email address compliance
• url address (wrapper for urlparse)
• slugifying input / alphanum special char regex
• punycode conversions

Sadly Pyramid doesn't have a similar validators library