Remove dashboard support for controlling document type field location

In the recent past, we spent time on several dashboard plugins to support controlling the location (column) of to-be-added document type fields. As the CMS document type editor can already do that (and also control the vertical position of a field), this functionality should not be duplicated, and should therefore be removed from the dashboard plugins.

This affects:

• selection plugin
• taxonomy plugin
• related docs
• tagging