Add DevGroupName command

[pcdiem]

Description:

Related issue (if applicable): fixes #<8082>

Add DevGroupName command and use the settings for the device group names instead of MQTT group topics. If a device group name is not set, fallback to MQTT Group Topic 1 (with the device group number appended for device group numbers > 1). This maintains compatibility with previous releases for all devices using device groups except those using the PWM DImmer module with remote device mode enabled.

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core Tasmota_core_stage
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.