Re-add params to IDragHandler
Re-add DragOperationsMask
Rename DragOperationsMask enum values
Apply flags attribute and implement `Every` option
Rename DragData properties
Populate DragData and pass through to IDragHandler
Revert change to .gitignore
Remove redundant handled variable
Change DragOperationsMask to uint and make Every = UInt32.MaxValue
Use uint instead of Uint32 for consistency (even though they're exactly the same)
Merge pull request #1 from amaitland/feature/draghandler

Feature/draghandler