Move Plaso image_export to imagetools

[joachimmetz]

As part of the effort to make parts of Plaso more reusable, move Plaso image_export to the imagetools project

• determine if artifact filter and pre-processing logic should be moved to a separate project
• filter based on artifact definitions
• filter based on single path - Worked on script to extract data streams #1 #98
• filter based on find specs (use YAML filter file?)
  • date and time range (image export --date-filter)
  • filename (image export --names)
  • filename extension (image export --extentensions)
• filter based on (content) signatures (image export --signatures)
• generate hashes.json output

[joachimmetz]

Maybe as a first step have Plaso image_export script use dfImageTools