Update lib to use V2 of log

[stefanthorstenson]

START_BLOCK_V2 is not implemented (still uses V1 start) added to the firmware are not yet in cflib

Log (port 5)

Control channel (5:1)

Command	Value	Constant	File	Defined	Used
DELETE_BLOCK	0x02	CMD_DELETE_BLOCK	log.py:79	Yes	Yes
STOP_BLOCK	0x04	CMD_STOP_LOGGING	log.py:81	Yes	Yes
RESET	0x05	CMD_RESET_LOGGING	log.py:82	Yes	Yes
CREATE_BLOCK_V2	0x06	CMD_CREATE_BLOCK_V2	log.py:83	Yes	Yes
APPEND_BLOCK_V2	0x07	CMD_APPEND_BLOCK_V2	log.py:84	Yes	Yes
START_BLOCK_V2	0x08	—	—	No	No — uses V1 CMD_START_LOGGING (0x03) instead

Suggest to update lib to use "Start block v2".

Note that calculation of LogConfig.period needs to be updated: