Attribute classname

Name: 'classname'
Since: draft
Usage on: 'Interface'
Allowed value: string with the exposed classname
Rationale: the javascript classname can deviatie from the interface name.
Default value: if this is not set, it is equivalent to the name of the interface name
Reference: 'Socket'

Example:

[ ImplementedAs=JSSocket,
  classname = Socket ] interface Socket {
};

class {{ cppclassname }} : public ClassMapper<{{ cppclassname }}>, public {{ classname }}_Base
{
...

class JSSocket : public ClassMapper<JSSocket>, public JSSocket_Base
{
...

// not needed