Infinite scale is a design principle

<!--HTML-->When working on the spaces feature we reorganized reva's internal path semantics. While the current global path based namespace looks efficient, it ties namespace organization to a single instance. This prevents true federation. By replacing absolute paths with relative paths and a corresponding root we can delegate building a user individual namespace to the clients. This allows them to present a more meaningful layout to the end user, even aggregating spaces from multiple instances. Furthermore, operations like quota, trash and change propagation now also operate on individual spaces. We are moving this approach forward on the "edge" branch and will propose changes to the cs3api to optimize the implementation. We consider spaces the logical next step in enterprise file sync&share.