ViSR: fix sizing of plots, get real feed from tomo camera

[Abigail-Yates]

This PR combines / replaces #158 #164 and #169 .

• Implementing pva to video to get the real camera stream: https://github.com/diamondlightsource/pva-to-video/pkgs/container/pva-to-video
• Plot sizing fixes:
  • Plots fill their parent box
  • SliceView plot resizes correctly when the controls drawer is opened and closed
  • Plots resize correctly when the window size is changed
• The size of the plots are calculated to use the remaining space after the controls drawer is opened
  --> i.e. when expanded, the controls drawer should show as full sized and the 'plots' should fill the remaining space without needing a scroll bar... until a certain minimum height for the plots is met (at which point a scroll bar appears)

[Abigail-Yates]

@tomkane-dls quick question - should this be in a different file? or should we be using the webcam from cs-web-lib as Emily suggested?
Is this intentional to keep it simple for testing?

[tomkane-dls]

Just to keep for simple testing so we always have an image to check the UI behaviour, but we will see the PVA stream if its working. We can remove later and work with Emily to use something like the Webcam later.