UI for eurostat_get in the viewer

[gdementen]

[gdementen]

Just a simple LineEdit with the indicator code would already help, but the full-blown browser I have in larray_editor/eurostat_index + larray_eurostat/index branches with a few modifications (open "branch" with a keypress (enter or space?), lineedit for fetching a known indicator) would be better of course.

[gdementen]

This should probably use common code with #188 (ie lineedit would filter tree instead of require entire indicator name).