ENHANCEMENT: allow disabling of Versioned prepopulate_versionnumber_cache

In large sites this can take a very long time, drastically slowing down the CMS
admin.  Even though the versions will then need to be queried individually,
this is still significantly faster than loading hundreds of thousands of
version numbers in one query and populating the cache array.
Merge pull request #2062 from jthomerson/enhancement_3.1_allow_disabling_prepopulate_version_number_cache

ENHANCEMENT: allow disabling of Versioned prepopulate_versionnumber_cache