TEMP: undo temporary commits

All dependencies have been released and we can now update to the latest
pom-imagej.
LegacyUI: implement createDisplayWindow

Copy and pasted from SwingSDIUI.
Use IJ2 to display text in LegacyUI

Instead of going through the ImageJ 1.x messages, let's use IJ2 to
display text. So LegacyTextDisplayViewer is no longer a
LegacyDisplayViewer, and will require the LegacyUI to create a display
window.