Custom templates for charts

[singerla]

Extract chart data from existing pptx files and use it as a template when creating a chart from scratch.

[singerla]

This PR also includes a fix for passing proper rId to chart. This allows creating multiple charts on a slide and/or mixed with images/links.

[heavysixer]

@singerla apologies for the late reply on this. First thanks for taking up this task and putting in the hard work here. @gregdolley there is a lot to consider here can we chat about this review?

[heavysixer]

@singerla apologies for the delay we're still discussing this internally.

[singerla]

@heavysixer don't worry, I can truly understand this PR isn't easy to handle :) You might want to at least cherry pick this, as it is required to insert multiple charts.

Please notice: The template based approach is perfect for my projects as they require a whole bunch of user defined settings. That's why I decided to start a template-only library: pptx-automizer.

I have learned many things here and I am thankful for the inspiration coming from your library! Keep on going!

[heavysixer]

@heavysixer don't worry, I can truly understand this PR isn't easy to handle :) You might want to at least cherry pick this, as it is required to insert multiple charts.

Please notice: The template based approach is perfect for my projects as they require a whole bunch of user defined settings. That's why I decided to start a template-only library: pptx-automizer.

I have learned many things here and I am thankful for the inspiration coming from your library! Keep on going!

@gregdolley let's please circle back around to this and resolve this one way or another.

[heavysixer]

@singerla as I am getting into your PR a bit more I think it's pretty clever how you support future chart types. I really like the fact that you can leverage charts in other files. One question do you think this approach will work for proprietary chart types like think-cell?