Extend SHT3x driver to work SHT4x (and GXHTV4) and allow multiple sensors

[MaxineMuster]

Sensors must be on different pins, for they share address 0x44

Additional sensors are added per command
SHT_AddSensor [sda-pin] [scl-pin] [chan_t= (optional, 0 if ommited)] [chan_h= (optional, 0 if ommited)] [type=3or4 (optional, autodetect if ommited)]

Sensors can be listed with
SHT_ListSensors:

Info:SENSOR:SHT_ListSensors: 2 sensor(s) registered:
Info:SENSOR:  [0] SDA=17 SCL=24 type=SHT3x   serial=0A29D08A  last T=21.2C H=45%
Info:SENSOR:  [1] SDA=28 SCL=23 type=SHT4x   serial=0AE1B59E  last T=21.4C H=46%
Info:CMD:[WebApp Cmd 'SHT_ListSensors' Result] OK

Most commands extended to allow an additional argument as "sensor" if there is more than one.

Will need some more testing, but basic function is working:

Probably GXHTV4 code will be removed later