Display an old version requirement.

This reverts commit f7d953d1eb2e3315d6b6b9d1f9ed217eaa22be6d.

And add 'for old versions' mark to the requirement.
Add contrib-clean to Grunt.

We should clean 'min' directory before build.
Add version number in minified sources.

Version number is parsed from package.json.
Before release, the version number have '-dev' postfix.
Merge branch 'master' of https://github.com/noraesae/perfect-scrollbar
rebuild