Remove section folding feature

[robhrt7]

Feature for folding separate sections was introduced long before Clarify, to allow better focus on currently developed component. Since now we have powerful alternative for this use case, and Clarify works really well for stand-alone testing, I propose section folding feature to be deleted.

[robhrt7]

This will also fix bug with typography markup which is not wrapped in p/div:

[ndelangen]

Might be better to move this feature into a plugin, if you think it's not useful by default. I use both the section folding and clarify when appropriate for my workflow. Clarify is my second choice when needing focus.

[robhrt7]

I will consider the possibility of moving it into the plugin, but seems like it's a redundant feature to have with the Clarify functionality.

Even plugin needs some maintenance. Having less redundant features makes software more stable and fit open source project a lot more nicely.