Anonymization of trajectory logs incomplete for v4.0

[keithoffer]

I noticed that while #161 added support for reading the new metadata fields, the anoymize log features weren't updated to remove the patient information. Unfortunately due to the strange way they setup that metadata field, there is no clear offset for the patient ID, so the whole metadata field will probably have to be read, adjusted, and then written with an anoymised patient ID.

Also, once the patient ID is written the CRC at the end of the file should probably be updated. From what I can tell, binascii.crc_hqx(insert_all_bytes_here,0xFFFF) should generate the right CRC.

[jrkerns]

Varian's implementation of metadata is indeed a bit strange but I should able to remove it. Thanks for the tip on CRC; I never worked on updating it because I was not aware of any software checking it after post-processing. I'll split these into two separate tickets.