old_contents: from viewflow.flow.base import This, Node                         # NOQA
  from viewflow.flow.end import End                                 # NOQA
  from viewflow.flow.gates import If, Switch, Split, Join, First    # NOQA
  from viewflow.flow.job import Job, flow_job                       # NOQA
  from viewflow.flow.start import Start, flow_start_view            # NOQA
  from viewflow.flow.view import View, flow_view                    # NOQA
  
new_contents: from viewflow.flow.base import This, Node                         # NOQA
  from viewflow.flow.end import End                                 # NOQA
  from viewflow.flow.gates import If, Switch, Split, Join, First    # NOQA
  from viewflow.flow.job import Job, flow_job                       # NOQA
  from viewflow.flow.start import (                                 # NOQA
      Start, StartViewMixin, StartFormsetViewMixin,
      StartInlinesViewMixin, StartView, flow_start_view)
  from viewflow.flow.view import (                                  # NOQA
      View, TaskViewMixin, TaskFormViewMixin, TaskFormsetViewMixin,
      TaskInlinesViewMixin, ProcessView, flow_view)
  
subject: Add mixins to export list. Close #50