Security-motivated dependency updates and related

[jrwdunham]

• Update dependencies motivated by security considerations

  • Bump pillow from 3.4.2 to 6.2.0 in /requirements
  • Bump waitress from 1.0.1 to 1.4.2 in /requirements
  • Bump requests from 2.11.1 to 2.20.0 in /requirements
  • Bump pytest to >=3.6 to fix testing dependency conflict (Travis)

• Added a Pylint directive to ignore a not-callable warning.

• Stop supporting Py3.4. Python 3.4 does not support Pillow >= 6.2.0 and that dependency seems to be a security requirement.

• Bump travis image from trusty to xenial

• Remove Py3.7 from Travis CI (needs resolution, see https://github.com/dativebase/old-pyramid/issues/32)

• Bump SQLAlchemy from 1.1.3 to 1.3.0

• Replace OurSQL dep with PyMySQL 0.9.2

• Catch SQLA InternalError in Search endpoint

  • New PyMySQL driver throws SQLAlchemy's InternalError (not OperationalError) when a malformed regex is supplied. Catch this error and respond as with OperationalError, i.e., 400.