Add support for zope.interface only, apart from twisted support.

Since twisted depends on zope.interface, each interface we defined in thrift file will be generated as a class derived from zope.interface if py:twisted option is enabled. This is great because we can treat implementations of these interfaces as components which can be registered in zope.component. However, sometimes we just only want to benefit from Component Object Model programming which is provided by the combination of zope.interface, zope.component and even zope.configuration, but not the deferred mechanism in twisted. So, besides option py:twisted, shall we add an extra option py:zope.interface ?