Added TM1637 support and more MQTT features

[giddyhup]

Added support for TM1637 seven-segment clock (e.g. to serve as a radio alarm clock).

Pins are defined in TM1637.h.

The colon between the second and third digit can be controlled via commands ("dotson" / "dotsoff"; e.g. to show that the alarm is active). Brightness can be controlled via command ("brightness=[0-7]"). These new commands report back via MQTT so that the clock's state can be stored (e.g. in Node RED) and restored via MQTT.

Added commands "realstop" and "realresume" to give finite commands and not just toggle the playback.

Added status message which is published when setup is complete ("ESP32 Radio is up.")

[giddyhup]

The idea is to have an internet radio alarm clock which can be remotely controlled (e.g. via a cron job). Of course, integrating the whole alarm function could be another approach.

Not yet included:

• state restore after reboot (the radio should not play on boot)
• pins, brightness, dots state settings via config