OJS is now upgraded to version 22.214.171.124, which seems to have solved the problem of icons not been always displayed. The new features enabled through plugins are: 1) Social sharing buttons in individual article pages; 2) preview of PDFs in the web browser with option to download the file; 3) Hypothesis.is shared annotaions support is enabled.
The third item need additional explanations. Hypothesis.is is a shared annotaion system based on open standards. Only a few days ago Highwire Press announced that it will adopt it for more than 3000 journals and eBooks. To use this system you will need to create an account at https://hypothes.is/ where you can also find information on aims and also use instructions.