Fix image stretch to fit behaviour

[NatLeung96]

I've added an objectPosition attribute, set to "top left", to the returned component. I believe the default behaviour is for this to be set to "center" which would explain the behaviour. I don't if it would be better for there to be an option for this?

[abigailalexander]

This looks good to me, I tested it in both Phoebus and CSStudio and the output image is aligned as we'd expect.
Slightly separate to above, but I also noticed that the sizing of the Image widget is slightly wrong in the web UI compared to CSStudio if stretchToFit=false.

CSStudio	cs-web-lib

As you can see the CSStudio one expands to fill the full dimensions passed to the widget, so we probably aren't setting our dimensions quite right. It would be good to fix this in this PR as well.

[NatLeung96]

I have now set the width and height of the div to always be "100%". Previously, they were only being set when stretchToFit was on.

[abigailalexander]

Looks correct now, thanks. Just one minor change to make

[NatLeung96]

I left that all there as I didn't want to affect the behaviour of img but actually it seems that the height and width of img can be set to 100% as well, with the only determining attribute being objectFit which is set by stretchToFit.