Date in copyright statement are only valid for EasyDiffraction

[arm61]

https://github.com/easyScience/easyApp/blob/bae8a781cfed7a8d8de130832c554614afbc7f9e/easyApp/Gui/Components/AboutDialog.qml#L131

This means that the copyright statement in EasyReflectometry has a start date of 2019