ENH: include error model plots in denoise-* output

[nbokulich]

Improvement Description
The error model plots output by dada2 can be useful for diagnosing issues with the model. This is used in tandem with the denoising-stats output to evaluate outcomes, e.g., too many reads lost at the denoising stage could indicate a poor error model. The plots output by q2-dada2 should be included in the outputs of denoise-* to assist with troubleshooting.

Current Behavior
No error model information is output.

Proposed Behavior
Include error model plots from plotErrors() as a separate tab in the denoise-stats output.

[gregcaporaso]

@jordenrabasco, any chance this would be something you'd be interested and available to work on?

cc @benjjneb

[jordenrabasco]

@gregcaporaso Yeah I am definitely interested! I am currently out of town until the end of the month, but then I should have a few weeks relatively free in early Aug where I can look into this. Does that work for a timeline on your end?

[gregcaporaso]

Definitely, thanks for your interest @jordenrabasco!