Make virus scanning configurable

We have added five new decision points covering all places in workflow
where ClamAV is being used. The processing_config module has been
refactor to acommodate for this new use case where a single user-facing
decision translates into multiple pre-configured choices in the
processing configuration XML document.

Co-authored-by: Jesús García Crespo <jesus@sevein.com>

.gitignore

@@ -2,6 +2,7 @@
 *.mo
 
 # IDE specific
+.idea
 *.directory
 .project
 .pydevproject