erp5_document_scanner: refactor code to reuse Base_contribute and create PDF with all images in background after submit

Use onEvent instead of addEventListener

For now, this is chrome only

/reviewed-on !944

bt

This reverts merge request !916

Merged by mistake

/reviewed-on nexedi/erp5!942

This reverts commit f9f020e3.

Assuming that the test database already exists and 'movement' table already
contains data (from past execution for example), on '--save' before this
commit:
  1. Create a new ERP5 Site:
     1. Install erp5_mysql_innodb_catalog.
     2. Call ERP5Site_reindexAll(clear_catalog=True) (from ERP5Generator.setupIndex()).
        => At this point, erp5_mysql_innodb_catalog tables are recreated.
  2. Install erp5_movement_table_catalog or any bt5 adding a new SQL table.
     => This does not recreate the table and leave the existing data as it is.
  3. Dump MySQL database to dump.sql.
  => dump.sql contains 'INSERT INTO' for 'movement' table *before* this '--save'.

This fixes random customer Unit Tests failures on SQL queries accessing
'movement' table directly and getting {non-existing,past executions}
Movements.

Fixes, refactoring, details and more app migrations.

/reviewed-on nexedi/erp5!916