Colorize duplicate rows in TM editor

[Anders Melander]

The TM editor currently displays rows using odd/even colorization both in normal and duplicate view.
When viewing duplicates the colorization should be changed so duplicate groups can easily be identified by their color:

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[Anders Melander]

Fixes #6: Duplicate rows are now colorized so grouping is perceptible.

→ <<cset 9949060feb03>>