Process units.xml data from CLDR, output units.txt
Also: remove unitPreferenceData from supplementalData.txt, moving it to units.txt instead. (Unit tests pass.)
Rationale: this makes the new units data available to units code under development. (Does this step already need a more formal proposal regarding the units work?)
(See the pull request - https://github.com/unicode-org/icu/pull/1173)
Please assign to me?