Drag cards to main area to make them sticky

[bergie]

Currently the UI cards in Dataflow can be made sticky by clicking the push pin icon in them. Instead of this, the interaction should be:

• By default cards are non-sticky, and appear on the left side of the screen based on the usage context the user is in
• To make a card stick, drag it outside of the left area to somewhere else on top of the graph
• To unstick it, click the X button

One question is whether the sticky cards should be position absolute, or position fixed.

[forresto]

The graph panning is actually a css transform, so if we wanted to put the
card somewhere specific in the graph it would take more work. I can see
uses for both, but more like fixed would be easier and probably more used.

[bergie]

@forresto good point, let us go with fixed then