This Merge Request adds 2 new bt5s:

• erp5_antivirus: it provides a basic workflow to track files that should be submitted (optionnaly) to an antivirus scan. There is no security set on the workflow. Files won't be scanned if they don't enter the workflow (setSuspect()), as not all files are susceptible to be corrupted (only the ones uploaded by untrusted sources). The charge of restricting accesses to infected documents is incumbent to each project, through local roles.
• erp5_antivirus_clammit: it provides the code necessary to run a scan on a document, by uploading it to a clammit service (deployed separately from ERP5).

(Requires slapos!1627 (merged))