Problem/Motivation
A very large vocabulary will cause the parent terms selector in "Relations" to hang a taxonomy term edit page. The page will typically load, but only after 5-8 minutes have elapsed.
Steps to reproduce
1. Build a large taxonomy list (95K entries should suffice).
2. Open the term edit page for one of these taxonomy terms.
Proposed resolution
Disable the parent terms selector function on taxonomy term edit pages for vocabularies containing more than "X" number of terms (perhaps 10K?). Parent hierarchies can still be selected through the Taxonomy Term overview page if needed.
