Add a Background Intelligent Transfer Service database parser

[william-billaud]

Add support for the %ALLUSERSPROFILE%\Microsoft\Network\Downloader\qmgr.db file. This file contains information related to the Background Intelligent Transfer Service.

• Structure comprehension base on https://github.com/ANSSI-FR/bits_parser + RE on qmgr.dll
• Do not handle the older (pre windows 10) format, maybe for later, but as Win10 is more than 10 year old, I don't thinks it's a priority.
• Do not make carving, as already existing tool (but it may be interesting, as the data format use a lot of known guid).
• Modify the UserRecordDescriptorExtension : no longer override field with None value. In this case its allows to keep the user_id value even if user is not found by the UserRecordDescriptorExtension
• PowerShell script used to generate test data is included in the test file.

Some reference :

• https://github.com/fireeye/BitsParser (post win10, support carving)
• https://github.com/ANSSI-FR/bits_parser (pre w10, support carving)
• https://cloud.google.com/blog/topics/threat-intelligence/attacker-use-of-windows-background-intelligent-transfer-service/

closes #1475