add support for folding headings and code blocks in the markdown editor

[ITProKyle]

Current behavior

# Headding 1

## Heading 1.1

```shell
echo "Hello world!"
```

## Heading 1.2

```shell
echo "Example 2"
```

Example text

Given the above note, all lines are shown in the code editor at all times. While fine for small notes, when a note has multiple headings/subheadings, it can be difficult to navigate.

Expected behavior

Adding the ability to fold sections of a note allows for easier navigation as large sections that do not need to be reviewed at the current time can be hidden from view.

# Headding 1

## Heading 1.1
## Heading 1.2

```shell
```

Example text

Ideally, each note would remember where its folded on a given device so that switching between notes would not unfold all folded sections. There should also be a way to fold/unfold all foldable sections of a note at once.

[Rokt33r]

We might be able to use foldcode addon of CodeMirror. https://codemirror.net/doc/manual.html#addon_foldcode

[Komediruzecki]

@Rokt33r thanks,

I'll add this to local space roadmap and try playing with the addons, if it works well we can implement/port it to cloud space as well!