Modify slide backgrounds about pptx-automizer

[singerla]

@MP70: Could you please provide a test case to this branch and probably some example code with your required parameters?

I would like to write some docs on how to create a new modifier. :)

[MP70]

Have added a little test. It's only a indicator, there may be a neater way to arrange it, like making the background another type like shape, table etc.

[MP70]

Currently manually getting the <p:bg> / <p:bgPr> element, then modify like:

bg
.getElementsByTagName('a:solidFill')[0]
.getElementsByTagName('a:schemeClr')[0]
.setAttribute('val', 'accent6'); // Change 'accent6' to your desired color value

[singerla]

Hi @MP70, please check out modify-master-background-color.test.ts to see a basic example.

[singerla]

@MP70: It would be great if you could also test modify-master-background-image.test.ts with your real world stuff. It turned out that a slightly different approach is required for background images compared to "normal" image elements on a slide.

@creedmangrum: This might be useful for you, too.

I'm happy about feedback on this!