docs(home): change grid with column spans

[DuncanFaulkner]

update the image for the grid, also created a stackblitz example for creating the grid, included an image of the source code as well. Source code now shows the grid created using the flex-layout library rather than flexbox and CSS.

I've included the images in a folder within the documentation, I would have preferred to have been able to do something like https://cloud.githubusercontent.com/assets/210413/20034148/ but can't see how to do that yet. If there some documentation on how to do this then I will amend this PR.

[DuncanFaulkner]

@googlebot I consent

[DuncanFaulkner]

@CaerusKaru is it possible to push this PR through or is there additional things you would like me to fix on this PR before it can be pushed?

[DuncanFaulkner]

Changes all complete, not sure why CI is not running again

[DuncanFaulkner]

Happy to create new samples so these can go on the Angular's stackblitz setup if required?

[DuncanFaulkner]

I think the CI is stopping this progressing

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