Error handling for onboarding and in general

[brushknight]

• [x] Handle MQTT connection failed, redirect user to enter MQTT data again.
  • [x] Allow x amount of retries before redirect.
  • [x] "Flush" MQTT setup before redirect.
• [x] Handle WiFi connection failed, redirect user to enter WiFi data again.
  • [x] Allow x amount of retries before redirect.
• [x] #81
• [x] #80