[Cdk-jchempaint] Help generation

[Konstantin T. <an...@ya...>]

HTML help in JCP has many drawbacks: many HTML errors, needs manual correction when icon names change, difficult to maintain translations

I propose to use HTML generation instead. I've added new target generateHelp, which currently executes class HtmlExample from src/util, it produces file example.html in dist/classes/org/openscience/jchempaint/resources/userhelp_jcp/en_US/example.html. It's almost identical to jcp.html, but:
a) is valid
b) style of contents could be easily customized since all elements are generated by function contentsEntry()
c) is potentially translatable with GT

But I couldn't set up i18n, GT produces crap (should return the same english strings because they have no translations)
Maybe, it's possible to use separate po directory for help translation

-- 
Regards,
Konstantin