Show statistics in laserpoints tab

[mzur]

In the laserpoints tab of the volume overview, show statistics such as "# images with successful LP detection", "# images with failed LP detection", "# images without LP detection". This could also be implemented with a pie chart (see project/volume statistics implementation).

The numbers can be fetched asynchronously via a new API endpoint when the tab is first opened. The UI could also poll the API endpoint for updated numbers or better (but more complicated) we implement websockets events in the LS detection jobs that the UI can listen for. Then users can start the LS detection and see live updates about the progress.