Render a basic FTB in the repository file tree + blob view

Summary

This is part of a bigger effort to implement a file tree browser (FTB) in the repository.

As part of this issue we should:

• Create a re-usable store, the store should later be promoted to a shared store, so don't couple it to the FTB
• Fetch the files and render them in the tree
• Indicate the current file in the FTB
• Implement filtering
• Navigate from tree → tree via FTB without refresh

Mockups

File	Tree