Update vehicle_thinkcity.c

First update. Tested on Think City with Zebra and gen1-PCU.
Update net_msg.c

Think City SMS printout trim
Update ovms.h

Added Think City specific variables.
tc_pack_temp is used because Zebra-battery operates at 270C which requires 9 bits.
Update vehicle_thinkcity.c

car_chargelimit_soclimit / _rangelimit set to -1 to avoid in the SMS printout in net_msg.c
Update ovms.c

Think City specific variables added
tc_pack_temp, tc_pack_voltage and tc_pack_current
Zebra battery operates at 270C and need 9 bits is been used in car_tbattery
Make car_tbattery signed integer, and integrate thinkcity changes