Add generic image widget

[fishrockz]

I was using this to make plots but it did not scale well.

I am trying a different approach but have been a bit side tracked but made some progress and would like to finish that too.

But this example may be useful to others/(me in the future) so I thought would push it up.

Most of the code is behind feature flags.

[cmyr]

Okay just a first pass, but this looks reasonable; I think it makes sense for there to be an image widget available, and this is a good start.

If we do merge this we will want to add documentation to all public items.

Thanks for the PR!

[futurepaul]

Thank you for tackling the various FillStrat options, that's been a todo on SVG that I haven't gotten around to. Perhaps after this lands we can add FillStrat to SVG and use the same type for both.

[fishrockz]

@futurepaul I had loads of changes to svg to allow embedded png/bmp images but it did not scale well enough for my use case. and trying to work out how it should work was hard. many of the references i looked at had different implementations. so i have not tidied it all up as i thought i would try to land this and see how much demand there was for the svg stuff, I am more than happy to look at the svg stuff if its useful.

[cmyr]

okay a couple more notes here, but looks pretty close to me!

[cmyr]

Okay a few more things I've spotted and a few comment fixes, we're getting close tho!

[cmyr]

Okay a few more doc fixes 😁

[fishrockz]

I have set this so maintainers can push the branch on my fork. I'm very dyslexic as you have probably noticed and have no issue with others pushing a typo fix etc.

[cmyr]

Looks good, thanks for your patience!