Add anonymise database task

[WithoutPants]

Occasionally, it is necessary to obtain a user's stash database for debugging issues. This PR provides a way for a user to share their database without leaking information they consider private.

Adds Anonymise, and Download anonymised tasks to the Tasks page - similar to the backup tasks.

Anonymise makes a copy of the database, randomising all sensitive data:

• deletes all image blobs
• renames all folders to be equal to their id numbers
• renames all files to be equal to their id numbers
• replaces fingerprint values with random hex numbers
• replaces non-whitespace characters of the following fields with random letters:
  • scene:
    • title
    • details
    • url
    • code
    • director
  • image
    • title
  • gallery
    • title
    • details
  • performer
    • name
    • aliases
    • details
    • url
    • twitter
    • instagram
    • tattoos
    • piercings
  • studio
    • name
    • url
    • details
    • aliases
  • tag
    • name
    • description
    • aliases
  • movie
    • name
    • aliases
    • synopsis
    • url
    • director