Support Mermaid markdown in Markdown card

[Pelicans-git]

Support for Mermaid in Markdown

The Markdown card is pretty useful, but it could be awesome if we could use Mermaid (https://mermaid-js.github.io/mermaid/#/) with it. The upside would be dynamic diagrams!

The following markup:

graph TD
    Raspi --> |Bluetooth| B(Temp Humidity 1)
    Raspi --> |Bluetooth| C(Temp Humidity 2)
    Raspi -->|Wifi| D[Sonoff 1]
    D --> E(Porch Light)
    Raspi -->|Wifi| F[Sonoff 2]
    F --> G(Garage Light)
    Raspi -->|Zigbee| H[Aqara Remote]

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would produce the following diagram:

By using templates, the diagram may be changed dynamically This would be huge!