Changing addthis code.
This affects both the setup html form in:
User Home > Journal Manager > Reading Tools > Configure AddThis
And also the sharing buttons apperaing in the footer.

Now, if the journal manager can enable/disable the new sharing buttons
instead of the old addthis code. Also the form has been simplyfied.
All the options that aren't used have been stripped.
Merge branch 'master' of github.com:eirikhanssen/ojs2.3.8.0-hioa-mod-journals