RSS2 feed generation in Plone 4.3 (Refs #14323)

- removing Products.fatsyndication support
- removing bda.feed support
- providing correct query for Plone 4.3 based syndication
Updating syndication related tests (Refs #14323)
Merge branch 'plone43'
Updating history
Adding conditions for Plone 4.3

This should preserve < Plone 4.3 compatibility.