Formatting in Lvl 1 and Lvl 19 Flowchart

[HungryBradbury]

• Interchanged the node shape between Yes/No nodes and Action Nodes, because while working on lvl 7 flowchart I found that the stadium shape of action nodes can't handle large text.
• Included class def for Yes/No nodes so that they change color with light/dark theme.
• Formatted some text in the nodes.

[HungryBradbury]

Okay, didn't realize if I pushed another commit while my PR was open it would add it to the PR.

So new addition - Level 7 Mermaid Flowchart

[Zamiell]

Okay, didn't realize if I pushed another commit while my PR was open it would add it to the PR.

yes, you need to start a new branch for that