force copy constructor to inherit plottingConvention

[vtvivian]

so if you do ebsd2 = ebsd1; you don't lose the plottingConvention set by ebsd1

Feature request: can we set the plottingConvention property explicitly in the @EBSD constructor (and do this for @EBSDsquare/hex as well, so that you don't lose this information after gridify?) (I am not sure how to do this correctly for a dependent property / child class.)