persistent live chat

[brandontyler]

The following pull request is to allow lex-web-ui to maintain the connection to Amazon connect chat session across browser refreshes.

*Issue # None

Description of changes: Following the suggestion of this readme: https://github.com/amazon-connect/amazon-connect-chatjs#handle-browser-refresh I added several state variables: participantToken: '', participantId: '', contactId: '', reconnectToActiveChat

To see if a previous live chat session exists.  If so then pass in the saved state variables into:
connect.ChatSession.create

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[atjohns]

Will review in detail later this week, however persisting sessions should be a control that bot developers can turn on/off and not tied directly to saveHistory