See and being able to download snapshots

[pirbo]

Show the "kappa ascii" text of snapshots in a dedicated tab (as for flux maps) + button to download them in dot/text.

That would be great to have a button "replace the current initial condition with this snapshot"

[pirbo]

I wonder whether "snapshot computation" can be a bit long and therefore should be interruptible...

[pirbo]

It would be nice to be able to export in text kappa ascii format:

%init: 100 A(x,y)
%init: 42 A(x!1,y!1)
...

[pirbo]

Last one is a dot format. It is outputted by print_dot_snapshot from main/outputs.ml