Infoelement crash fix and cleanup

• do not retransform, because it is done already in the Cartesian Plot. Retransform will crash labplot, because in retransform the plot datarect is used. Which would lead to a crash
• Check that setText does not call texlabelTextChanged of the infoelement, because this leads also to a call of retransform and the application will crash
• remove xPos, because positionLogical exists
• supressChildPositionChanged if the position of the custom point will be changed by the infoelement
• move connects to the end, otherwise position changed of the custompoint will be called
• position.point returns the position in scene coordinated and not the logical position which is stored in positionLogical()