Suggestions for Publons plugin

[asmecher]

See the various commit messages. These might need to be ported to other branches too. They're mostly cosmetic, but do fix a possible escaping problem around POST parameters to the API.

[asmecher]

Some suggestions for further tweaking:

• Some adaptations will be needed in the master branch in for when OJS 3.2 is released. For example:
• The master branch now uses Smarty v3, and some of their function names have changed (e.g. for registering output filters)
• The conventions around naming template files have changed
• The plugin assumes that English content will be available, but that may not be the case.
• There might be some quirks in the JSON encoding? I'm not sure about the use of JSON_UNESCAPED_UNICODE.
• Purely cosmetic, but there's a bit of a mix of space-based and tab-based indents. Use whatever you're comfortable with, obviously; we generally use tab-based indents.
• There appears to be some dead/unused code, e.g. the getPublonsReviews function.