Improve interactive mode

[kasnerz]

Currently, only a very basic version of the interactive mode is implemented (#4). The user can enter edit mode, change cell value(s), and re-run the pipelines.

Only the edited cell ids are sent to the backend (together with the new values) & an altered version of the table is created for the current request. This way it should be relatively safe since the dataset will still contain the original, unmodified table.

TODO:

• invalidate / hide pre-generated outputs
• investigate if the current approach is safe enough
• think about persistence - should we keep the edited values after a new table is fetched?