Re-split ajaxEnabled into ajaxLinksEnabled and ajaxFormsEnabled

[jblas]

A few folks have chimed in since scottjehl landed this fix:

8929ac3

which merged ajaxLinksEnabled and ajaxFormsEnabled into a single ajaxEnabled config option. They have specific use cases where they need the options to be split again.

[jaspermdegroot]

Closing as feature request and added to the wiki page.