Rework button handling, device announcement

[an-erd]

since there is only one button available, the function of this button needs to be clearified:

• switch to next screen maybe:
• in a config screen -> long press to reset BLE devices?
• on a specific screen -> long press to remove this particular device
• announce a new BLE device when being very close (using RSSI)
• add MQTT screen and in the MQTT screen long press to turn on/off sending MQTT messages

[an-erd]

RSSI when getting close to the Proxy, so ~ -25 - -27 would be a good threshold

I (4157) BLEMQTTPROXY: (0x00070002) rssi -47 | temp  22.4 | hum  38.1 | x  +9218 | y +22781 | z +17087 | batt 3030
I (5157) BLEMQTTPROXY: (0x00070002) rssi -48 | temp  22.4 | hum  38.1 | x  +9218 | y +22781 | z +17087 | batt 3036
I (6157) BLEMQTTPROXY: (0x00070002) rssi -49 | temp  22.4 | hum  38.1 | x  +9218 | y +22781 | z +17087 | batt 3036
I (7157) BLEMQTTPROXY: (0x00070002) rssi -44 | temp  22.4 | hum  38.1 | x  +9218 | y +22781 | z +17087 | batt 3036
I (8157) BLEMQTTPROXY: (0x00070002) rssi -25 | temp  22.4 | hum  38.1 | x  +9218 | y +22781 | z +17087 | batt 3036
I (12157) BLEMQTTPROXY: (0x00070002) rssi -25 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (13157) BLEMQTTPROXY: (0x00070002) rssi -26 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (15207) BLEMQTTPROXY: (0x00070002) rssi -24 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (16177) BLEMQTTPROXY: (0x00070002) rssi -27 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (17207) BLEMQTTPROXY: (0x00070002) rssi -29 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (18207) BLEMQTTPROXY: (0x00070002) rssi -45 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036
I (20207) BLEMQTTPROXY: (0x00070002) rssi -23 | temp  22.4 | hum  38.1 | x +26631 | y -13586 | z -11071 | batt 3036