Use Indigo installed version of python Cryptography Package Code improvements

The Starling Plugin can only turn on or off the Nest Thermostat's Hot Water Boost. Now, the standard Indigo Turn On | Turn Off commands will keep the hot water turned on until turned off by using a timer to send a repeat turn on command before the boost timer is cancelled, thereby resetting it to continue boosting. The repeat turn on command is output to the Indigo Event Log. A new action has been added "Boost Hot Water" which will now just do an ordinary boost, e.g. the Hot water will turn off after the default boost time. Turning off the Indigo Hot Water device, will cancel the boost.

Added a requirement to update Cryptography package to version 39.0.2

If the Cryptography package vesrion is older than 39.0.2, th eplugin will be stopped and you will be asked to run the following command in a terminal session:

pip3 install --upgrade cryptography

The plugin icon has been corrected.

Release for Indigo Plugin Store

Include check for missing API Key and also for an API Key entered with an embedded New Line character which is invalid.

Important: Python package cryptography is required. Run command 'pip3 install cryptography' in terminal.