Fixed possible licensing issues

This backports various commits from master, which might  fix some issues from licensing perspective:

* Use jQuery.datepicker for date/time parsing/formatting instead of date.js.
* Do not minify all javascript files on release.

The date.js file has problematic license and we already ship code for date/time parsing in jQuery datetime picker plugin, so was quite easy to replace the few functions.

Minification of javascript on release time is problematic as according to GPL we should ship code in preferred form for modification, what minified code is not.