Export : find a solution to export samples having no LAT LON

[picheral]

linked with #57

A solution could be to export them when the selection of the samples is created via the selection of a unique project and not via the selection of a geographic area.

[jiho]

Agreed.

[grololo06]

To generalize a bit, the data export shows first a choice panel:

which comes from queries on the DB and EcoTaxa API calls.
I think it's doable to add that, if any referenced project has unlocated samples, we add a checkbox to let user specify that they want as well, in their exported data, related but unlocated samples.
Or a checkbox per project for full flexibility.