The web client never calls Plugin.done() when doing contexts check

[Nicklas Nordborg]

In /www/common/plugin/index.jsp there is code that checks if a plugin can be used in a given context or not (by calling InteractivePlugin.isInContext()). This code lacks a call to Plugin.done().

Also, I think that the context checking code should be moved into the core. I think there is similar code in other places which could reuse the core code.