global: fix handling of debug and simplify toolbar

* Fix issue where runserver manage command would not enable the
  Werkzeug debugger.

* Changes how debug-toolbar is enabled via only DEBUG and EXTENSIONS
  configuration variables.

* Fixes issue in legacy module that would override app.debug with
  value of CFG_DEVEL_SITE even though DEBUG had been set in
  configuration.
registry: move to separate package Flask-Registry

* Moves Flask-Registry to a separate external package.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>