Iterative connect

• Implement iterative connect to allow for dependencies between components at initialization
• Make adapters forward None if no data is available
• Use FinamNoDataError to represent missing data (bubbles up through adapters)
• Add tests for successful iterative connect, as well as for fail due to circular dependency
• Update docs (see finam-book!23 (merged))

Fixes #28 (closed)

Usage in a component:

    def connect(self):
        try:
            pulled = self._inputs["Input"].pull_data(self.time)
        except FinamNoDataError:
            self.status = ComponentStatus.CONNECTING_IDLE
            return

        self.status = ComponentStatus.CONNECTED