New module: metaDMG

[fgvieira]

• This comment contains a description of changes (with reason)

• There is example tool output for tools in the https://github.com/ewels/MultiQC_TestData repository or attached to this PR
• Code is tested and works locally (including with --strict flag)
• docs/README.md is updated with link to below
• docs/modulename.md is created
• Everything that can be represented with a plot instead of a table is a plot
• Report sections have a description and help text (with self.add_section)
• There aren't any huge tables with > 6 columns (explain reasoning if so)
• Each table column has a different colour scale to its neighbour, which relates to the data (eg. if high numbers are bad, they're red)
• Module does not do any significant computational work

Add module to plot metaDMG results.

[vladsavelyev]

We want to avoid including extra heavy dependencies as much as possible, and so far got away without pandas 😅 Wonder if it would be easy to use csv.DictReader here and operate on dicts?