Revert "Replace the treetwisty.svg with a png"

This reverts commit 505cb07f1849114fc0b43ac7a8b9d91922d2a90e.
Revert "Revert "Replace the treetwisty.svg with a png""

This reverts commit cb1627ee935c8f703b42abd14756e6d9f560068b.
Capture the mouse during histogram selection dragging.
Merge pull request #28 from mstange/histogram-mousecapture

Histogram mousecapture