docsite: Make Evy snippets editable and runable

[juliaogris]

In the docsite make Evy code snippets editable and runable

• Run (will change output in output section)
• Revert (return to original code)
• Copy (copy current code)

```evy blocks => evy editor
```evy:out    => target output
```evy:in     => source for sample input editable