Add file sidebar tab

[julien-nc]

closes #158

Some approval-related content was previously injected in the sidebar. This is not possible since NC 28. It is still nice/important to see and change approval-related stuff in the sidebar, for example, when a file is opened in the viewer, we don't see the file list anymore.

This PR adds a basic sidebar tab that contains the same thing as the modal that opens when clicking the inline approval status in a file list item.

• Modal after inline status click (was there before):

• Sidebar tab (new stuff):

@skjnldsv Slightly off-topic:

• Any way to ask for a file list item refresh when we don't have a reference to the node object? Something like emit('files:node:updated', node) but only knowing a file ID or file path.
• Any way to ask for a sidebar refresh? Looking for something to trigger all tab's update(fileInfo) method call.