User should be able to navigate upward in the hierarchy. Please take a look at the [prototype](https://href.li/?https://www.figma.com/proto/SptxS8feaNYtWUzoeNM4qI/Nested-Blocks-i2?node-id=2%3A9167&viewport=-1433%2C80%2C1&scaling=min-zoom) to get a sense of how it should behave. User should be able to navigate upward in the hierarchy by tapping the Up button inside the floating toolbar. <img width="492" alt="Screen Shot 2019-08-22 at 21 28 04" src="https://user-images.githubusercontent.com/5032900/63539901-c15aee80-c523-11e9-964e-b2a5da9758a7.png">