Multiple Block Mangers

WARNING READ and FOLLOW next 5 steps, then REMOVE them before posting the issueFollow CONTRIBUTING Guidelines https://github.com/artf/grapesjs/blob/master/CONTRIBUTING.mdUse the GitHub Issues EXCLUSIVELY for BUGS, FEATURE REQUESTS or QUESTIONS. Prefix the title of the issue with its context, eg. [Bug]: ....Do a quick SEARCH first, to see if someone else didn't open the same issueDON'T ASK to create examples/code for you, read DOCS and APIs first, then you can post what you have tried (we'd like to see your code) and what you're unable to achieveAll relative statements/questions have to be fil...