Upgrade for Python 3

[zevaryx]

Upgrade to support Python 3

Drops support for Python 2, but since Python 2 has been deprecated, this should not be an issue

Known Issues

• UnicodeDecodeError about wrong starting byte when opening some logs
  • Error handling for this error needs added. This wasn't an issue before due to Unicode not being native in Python 2

[Jahaja]

Thanks for the PR. What's the reason for the bootstrap version bump?

[zevaryx]

The Bootstrap version bump was due to Flask dropping support for Request.is_xhr, and to bundle all of the required JavaScript in a single file in bootstrap.bundle.min.js for all of the functionality. The bundle file wasn't an option in Bootstrap 3, and is new to Bootstrap 4