Pre-download interaction input data before display.

This make interactions much more self-contained because now everything that an
interaction requires is downloaded from Taverna Server before being displayed in
the browser. This means we no longer need to proxy data downloads through
Taverna Player and all contact with Taverna Server is once again kept within the
delayed job worker code.
Remove the remaining interaction proxy machinery.

No longer using it, so no longer need it.
Remove the AJAX get data function from interactions.

We should not need this any more as all interaction proxying is encapsulated in
the delayed job worker.
Rename the interaction output_value column to data.

This is because it is being used for both input and output data now not just
outputs.
Merge branch 'rh/int-data'

* rh/int-data:
  Rename the interaction output_value column to data.
  Remove the AJAX get data function from interactions.
  Remove the remaining interaction proxy machinery.
  Pre-download interaction input data before display.