Increased performance for sorting backlogs

The drag and drop operation is now more fluent for large backlogs.
The outerWidth and outerHeight functions had to
be overridden with a check for display:none-items since calls on
such items were the bottleneck.

fixes sonyxperiadev/BacklogTool#104
Increased version number
Merge pull request #106 from fredrikpersson/master

Increased performance for sorting backlogs