Add new static image for tooltip and use it
made toposhop link layer-dependant
Merge pull request #587 from geoadmin/data_#1334_New_Attribution

External link image missing tooltip
Disable snapshot service (500 error always)
Merge pull request #589 from gjn/dev_error_snapshotservice

Disable snapshot service (500 error always)
Merge pull request #588 from geoadmin/ltfoa_small_fixes

made toposhop link layer-dependant