Sanitize data that is exported

[blurymind]

I received some reports from Gdevelop users that their yarn exported json files were crashing the bondagejs parser. Some of these visualnovel developers using yarn like to copy stuff from the web and paste it into their dialogue, then save that.
Unfortunately they may copy some invalid characters or even ones that are invisible and pass that off to the game engine, where the bondagejs parser will crash.
People encountering this issue tipically create a new yarn file and paste their dialogue into it in order to fix their issue.

I suggest adding some sanitation when yarn saves files or dialogue nodes - to clean them up from crap data that would corrupt the json file.

Additionally sometimes putting spaces or odd characters when entering node names also leads to problems- so maybe the node title field needs to be validated too

Might do a PR, but would like to get some feedback first