Attempt to fix devices / trackers going "unavailable"

I believe this should fix the issue of devices disappearing or going unavailable on a regular basis.

Fixed "Traffic" Key issue.

Fixed issue #40 / #43 related to "traffic" key errors.

Add Version Key for Manifest File

Add version key for manifest file.

Update Default Unit of Measure to Mbit/s

Google Wifi reports unit of measure on Speed Tests in Mbit/s. Updated the integration to reflect that. Displayed Unit of Measure can still be changed in Integration Options (requires restart).

Minor changes - Default Polling Interval and System ID Attribute

Updated default polling interval to 30 seconds to try to address stability issues on some systems.

Added system (system_id) as an attribute to all sensors/device trackers etc. for users with multiple systems.

Dynamically add new entities as new devices connect to Wifi

Previously new entities were only added when Home Assistant started so new devices which connected to your network for the first time would not be created until the next restart.

This update now dynamically will create the new entities as devices are connected and should also dynamically delete entities which disappear from the Google Wifi Cloud (which have not connected in a very long time).

Fix intermittent stationMetrics error.

Fix an error that may intermittently show up in the logs related to stationMetrics.

Fix for multiple systems and prioritized device attribute.

Fixes an issue for users who own multiple Wifi systems where the integration would only return the first system.

Also fixes a small issue where the prioritized attribute flag would not reset after the prioritized period ended.

Fix issue with error for sensitiveinfos in Home Assistant logs.

Bump googlewifi library to handle issue with sensitiveinfos showing up in error logs.