Support wysiwyg fields for blocks

[javihgil]

In Librio CMS Improvements there are 2 mentions to something like this:

CMS block with page blocks: Sorry about that, took me a while to remember what I meant. What would improve drastically the way we work is to have the CMS edit capability also inside de blocks. So instead of having a basic textarea or a textfield in there we could have a full page block (image left or right, bg colour, title and text) that we could reuse for different pages later. That way, things like the voucher module that we added for Xmas could be done once and then add the full block the pages that we want with a schedule. It's similar to the previews one (CMS block should have wysiwyg and channel and locale?) but a bit more advanced.