Remove imports of treebeard from settings/base.py - redundant as current wagtail provides its own copy of treebeard
remove treebeard submodule
Remove redundant imports of modelcluster from base.py; install modelcluster 0.1 instead
Remove django-modelcluster submodule
add a pinned git version of wagtail to requirements, and remove the import from base.py
remove django-wagtail submodule