require careportal to be enabled
clean up the setting of env vars and  better support azure weirdness
lower case the ENABLE env var value to prevent support pain
fixed bug that caused the ENABLE env to not be read if set as a Connection String in Azure
make sure env.enable is set before trying to use it
the careportal is only enabled if the api is also enabled
Merge branch 'dev' into wip/enable-careportal
Merge pull request #142 from nightscout/wip/enable-careportal

Change to require the careportal to be enabled before use