Add UglifyJS

Add a JavaScript parser/compressor/beautifier as submodule:

https://github.com/mishoo/UglifyJS

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>

.gitmodules

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+[submodule "uglifyjs"]
+	path = uglifyjs
+	url = https://github.com/mishoo/UglifyJS.git

uglifyjs

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+Subproject commit ef4d776aedee6cbc8959a8e76403b82523615d3a