support for remote vtkpython analyses

Instead of performing VTK analyses on the client, I am now
experimenting with being able to perform them remotely, as we
have been doing for R.  This code is mostly untested at the moment,
so follow-up commits are likely.
allow users to select multiple inputs

Change the way the DataBrowser operates so that users can
select more than one item at a time.  This change was made
to better support analyses that require multiple inputs.

As a result, changes were also made to the functions involved
in the running of analyses.  Lots of these functions took
in a single DataModelItem as a parameter.  In these cases,
the parameter was changed to accept a list of such items
instead.
AnalysisServer changes for vtkpython

This commit contains changes necessary to get the vtkpython
celery task running successfully.
Merge branch 'vtkpython-remote'

* vtkpython-remote:
  AnalysisServer changes for vtkpython
  allow users to select multiple inputs
  support for remote vtkpython analyses
Merge branch 'master' of git://visomics.org/visomics