Improve reconfiguration in web-configuration

[zehnm]

With the Integration-API v0.8.0-beta there's now a reconfigure flag in the setup_driver message for setting up the integration.
This is used in the web-configurator in the "edit integration" screen.

When reconfiguring the HA integration:

• Access token should be optional, to make it easier for the user to change other options:
  • If left empty: use existing one
  • Only overwrite existing token if a new token is provided