Time comparison to 'never' fails for admin update notification

[sheagcraig]

Describe the bug
Sal UI dies trying to compare 'never' to a float epoch time.

Traceback:

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
39. response = get_response(request)

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _legacy_get_response
249. response = self._get_response(request)

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
187. response = self.process_exception_by_middleware(e, request)

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
185. response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/usr/local/lib/python3.6/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
23. return view_func(request, *args, **kwargs)

File "/home/docker/sal/server/views.py" in index
79. context.update(utils.check_version())

File "/home/docker/sal/server/utils.py" in check_version
170. if current_time > next_notify_date:

Exception Type: TypeError at /
Exception Value: '>' not supported between instances of 'float' and 'str'

Example values:
current_time: 1544108664.4966092
next_notify_date: 'never'

To Reproduce
Steps to reproduce the behavior:

1. Possibly not an issue on other versions; certainly an issue on the 4.0 branch...
2. New version is available.
3. "never" is chosen as the remind me option.
4. Try to view something.

Expected behavior
You're not nagged again until the next version and the site works correctly.

Server (please complete the following information):

• Docker, py3/sal 4 branch

[sheagcraig]

Fixed by #305