Avoid collision of status flags in tree items when updating tree nodes

Fixes silverstripe/silverstripe-cms#445
See https://github.com/silverstripe/silverstripe-framework/pull/1996
Thanks to Jean-Fabien for getting this started
Merge pull request #2014 from chillu/pulls/445-tree-statusflags

Avoid collision of status flags in tree items when updating tree nodes
Add explicit extension trigger to preview iframe updates.
Merge pull request #2016 from mateusz/preview-trigger

Add explicit extension trigger to preview iframe updates.
BUG Fixing missing </div> and </button> in UploadField_uploadtemplate
Merge pull request #2020 from halkyon/uploadfield_missing_end_tags

BUG Fixing missing </div> and </button> in UploadField_uploadtemplate