Add option to toggle code folding

[jaesharp]

Add an option to disable code folding entirely as it is not always desired by all users. This PR is a strawman for suggestions to enable more detailed code folding options. It is likely not ideal and probably doesn't work correctly (in terms of re-enabling and toggling on the fly) -- it works for me but I'm new to IntelliJ extensions, so criticism is more than welcome and probably quite mandatory.

[jaesharp]

Is there any interest in this PR?

[jashelio]

Yes, please. Current code folding seems arbitrary, and even if it were done "well" I'd rather default to none at all.