adding delay before positioning tiles in the viewer, see #6850

this will prevent from loading tiles when user triggered another action
for example: if user zooms using mouse-wheel it will load only
tiles from the final level rather then all levels
adding delay value to the vieport
fixing delay param in bird eye, close #6850
Merge pull request #1529 from aleksandra-tarkowska/6850_loading_tile

6850 loading tile in big image viewer