Short description to update the current lib

1. Go to https://github.com/uxsolutions/bootstrap-datepicker
2. Download latest release (dist-zip-file) and unzip that file
3. Copy all files in this libs/bootstrap-datepicker/ folder
4. Rename bootstrap-datepicker.zh-CN.min.js to bootstrap-datepicker.zh.min.js to be compatible to our language string
5. Change within that file the string a.fn.datepicker.dates["zh-CN"] to a.fn.datepicker.dates["zh"]
