Enable Shadow DOM by default #119
Description
CodeFlask depends on specific CSS in order to keep sync between <textarea>, <pre> and <code> blocks.
More than often, users face issues were a project already has imperative CSS code that styles those elements, and this leads to misconfigurations in CodeFlask editor instances (aka. Page CSS leaks into CodeFlask elements).
A good way to prevent this is using Shadow DOM whenever creating a CodeFlask instance, so there is no risk of CSS leakage in or out the editor.