Fix issues with blur event and richtext tile (alternative) [3.0.x]

[petschki]

Fixes:

• blur event on every click outside a selected tile
• prefill new richtext tile with default_value when creating it
• re-enable placeholder for empty richttext tiles

this supersedes #548

[petschki]

@frapell I came up with a different approach to #548 here: let tile.setupWysiwyg() take care about prefilling with default_value ... and I realized that the placeholder option can now simply be a string so its placed again when the richtexttile is empty.

Also the amount of changed chunks in your PR scared me 😄 If I do yarn upgrade&&yarn build I get 4 changed chunks instead of +4k in your PR ... I do not really know why though. maybe there's a local path saved somewhere and this is different to my machine?

@thet you might know why in detail?

[thet]

@frapell @petschki out of my head I can't tell why there are so many different chunks. Maybe you need to do a yarn install --force? Maybe the @patternslib/dev version is the one where we had those chunk generation issues.