Remove Commons (lang, collections, IO) dependencies

[grgrzybek]

#2131 shows a problem with private-packaged commons-io libraries.

After I checked, I see that only two methods of one class are used (FileNameUtils), so we don't really need that.
Also I see we no longer need (but the Private-Package is still there) Commons Collections 4.

And org.apache.commons.lang3.StringUtils.isNotBlank() is really something that doesn't require a dependency! (added in 3260bd2).