[IMP] base,mail,web: attachments adaptation for documents

This commit is the counter-part of an enteprise commit introducing
the Documents app.

Here is a summary of what has been done:
  - tweak unlink of ir_attachment to prevent unlink recursivity
    (when attachments are attached to ir_attachments)
  - improve ir_attachment kanban view
  - add several arguments to binary_content controller:
    - 'force_ext': to force the extension in the filename, base on
      mimetype
    - 'share_token' and 'share_id': to autorize download from a
      share link
  - add 'thumbnail' field on ir_attachment to optimize Kanban view
  - add 'upper_limit' argument to image to allow to bypass the
    500*500 size limit
  - DocumentViewer now handles text files

More information available on task 1853490

Co-authored-by: Pierre Paridans <app@odoo.com>
Co-authored-by: sri-odoo <sri@odoo.com>
Co-authored-by: ThanhDodeurOdoo <tso@odoo.com>