add [!] warning symbol to edited values with warnings

[dericed]

For instance open a valid wav file and set "Originator" to 😎. The interface will show a warning because of the non-ascii character. Close the edit interface and the warning about the issue is not-visible, just a green cell to be saved. I suggest here to overlay an orange exclamation point over the right edge of the field with a mouse over of the same warning message shown in the field-edit ui.