Data Bucket Stream is usefull when storing data from many small files

/reviewed-on !6

(cherry picked from commit 416502dc)

Conflicts:
	bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.IngestionPolicy.py
	bt5/erp5_wendelin/TestTemplateItem/portal_components/test.erp5.testWendelin.py

(cherry picked from commit 1ca48658)

This allows to set all kinds of arrow properties while keeping the main view simple.

The previous implementation did not support saving categories in view form.
It is better to use standard Base_edit in view forms and put actions which are other than "save"
into a dialog.

getArrayDtype can be used for example by html5 app to display graph with correct dtype

data model: split ingestion policy script (tag parsing) form ingestion operation (writing to data stream)