Change comparison in getPositionOfItem in UserVariableAdapter

After copy ''item'' would be a different object. As we only want to know
the position of ''item'' in the adapter a comparison of the names is
sufficient.
Fix selection of ChangeVariableBrick's Spinner after copying a Sprite
Fix testUserVariableSelectionAfterCopySprite
Merge pull request #465 from Catrobat/CopySpritesObjectVariables

Copy sprites object variables
accepted by @sjaindl, @robertpainsi and @felly