End time in search for playback range not expected format

[aywaldron]

This line throws an error because end_time does not match the expected format:

AIT-GUI/ait/gui/__init__.py

Line 1082 in bff6cd7

dt = datetime.strptime(end_time, '%Y-%m-%dT%H:%M:%S.%fZ')

To replicate:

1. Check out branch issue-142 and use latest updated master branch of AIT-Core
2. Update config.yaml to contain the following:

plugins:
    - plugin:
         name: ait.gui.AITGUIPlugin
         inputs:
              - telem_stream
              - log_stream
         outputs:
              - command_stream

    - plugin:
         name: ait.core.server.plugins.DataArchive
         datastore: ait.core.db.InfluxDBBackend
         inputs:
             - telem_stream

3. Run ait-server and navigate to localhost:8080
4. Run ait-example