Fix config entries are only applied when their values evaluate to true (#65)

Checking whether a config entry exists is currently done by checking if their value evaluates to true after type conversion. This is for example a problem when trying to set carbonDioxideThreshold to 0.

'awair-pm' IAQ method update

[Enhancement] If awair-pm selected, Glow and Glow-C will use awair-aqi method with configured endpoint and limit.

Add awair-pm Air Quality Method

Add awair-pm 'air quality method'. When 'awair-pm' selected, the HomeKit Air Quality tile only reflects the particulates value, which is useful for automating air purifiers.

Updates to README.md and Config Schema

• [Enhancement] Update config schema titles to provide better description and consistency across titles.
• [Enhancement] Update README.md to be consistent with config schema changes. Clarify that when upgrading from 5.6.4 to 5.7.x that you should first uninstall plug-in, reboot, reinstall, configure and reboot. This is due to change in device accessory cache format.

Introduce Display and LED controls for selected models

v5.7.x of the plugin introduces control of the Awair device display for Awair Omni, Awair r2, and Awair Element. Reference Wiki for details and examples of HomeKit automations for this feature.

When migrating from v5.6.3 to v5.7.x please first uninstall homebridge-awair2 (copy your Developer Token first), restart Homebridge to clear 'homebridge-awair' cached accessories, install homebridge-awair2, add your Developer Token, and finally restart Homebridge one more time.

Update carbonDioxideThreshold default values

Change carbonDioxideThreshold default from 0 to 1000 and carbonDioxideThresholdOff default from 0 to 800.

Add new images to screenshot folder for Awair2 Wiki.

New install updates

While performing a new install on Raspberry-Pi 4B it was found that changing 'placeholder' values to 'default' in config.shema.jsan provided a simpler installation.

Added check that carbonDioxideThresholdOff is less than carbonDioxideThreshold. If not, set to default values.

Housekeeping

Remove unused functions (getLocalData, getLocalConfig, getApiUsage).

Correct Awair device type

Correctly define Awair devices as 'air quality monitor', not 'air purifier'.

Add NowCast AQI support

• Add NowCast-AQI airQualityMethod for Omni, Mint, Awair, Awair-R2 and Element. NowCast-AQI fixes endpoint to 15-min-avg and data points returned to 48 (12 hours) for these devices. For Awair Glow and Awair Glow C, airQualityMethod is set to awair-aqi with same fixed endpoint and data points returned.
• Correct Awair, Glow and Glow-C reporting of PM25 which is not available on these devices. NOTE: Installed devices need to be removed from Homebridge followed by reboot to correct. Individual devices can be removed through Homebridge UI settings.
• Update config.schema.json to conditionally show options based on prior entries.
• Logging clean-up.