optimize the updating aqi data sql
update the json debug code
send welcome message when someone add pi as contact
add aqi level message
Merge branch 'exp' into v0.8.13
Merge pull request #26 from NoahShen/v0.8.13

V0.8.13
1. optimize the updating aqi data sql
2. add aqi level message
3. update the json debug code
4. send welcome message when someone add pi as contact