Added text selection and copy support to TextFieldWidget.

Use Shift and navigation key (cursor, home, end) to select a portion of
text, and replace/delete/cut as appropriate.
Also provides support for selection with mouse (click and drag)

mods/ts/metrics.yaml

@@ -2,3 +2,4 @@
 Metrics:
 	ColorPickerActorType: mmch.colorpicker
 	ColorPickerRemapIndices: 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31
+	TextfieldColorHighlight: 1a1a1a