Disable folding if isFoldEnabled config is false.

(This replaces previous PR #3740).

Allows the disabling of Code Folding. This attempts to solve Issue #3709.

This PR adds a config to check if folding is disabled.

Tasks:
- [x] Disable Code Folding in Gutter if config item is set to be disabled (and unfold all when disabled to show all code)
- [ ] Disable/hide Folding menu if config item is set to be disabled
- [x] Add place to configure if folding is enabled or not - this can be added to users' config file (added to config-schema)
- [ ] Add scoped configuration
- [ ] Ensure no other places enable folding...