Handle pasted content

[ellatrix]

• adds TinyMCE's paste plugin.

[aduth]

Is there some context for this that you can share?

[ellatrix]

At the moment this is more of a proof of concept.

• The plugin strips unwanted attributes id, style and class from externally pasted content.
• If the pasted content is inline, it will let the content be pasted in the block at the caret position.
• If the pasted content is one block or more, it will parse the content and insert it after the block.

To do's:

• Parser does not recognise blocks without delimiters, so at the moment pasted block content will be dumped in a freeform block. Cc @nylen.
• Block content is inserted after the selected block rather than at the caret. Ideally the block should be split if possible and the posted content be inserted in between.

Apart from that I think this is a good improvement for paste...

[ellatrix]

Redoing this a bit since the single paragraph approach was merged. This would allow us to do the following:

• If the pasted content is inline, insert it at caret position. In other words, don't do anything special.
• If the pasted content has blocks or block level content, split the text block at the caret, parse the content, and insert it between the split content.

[ellatrix]

Partly merged, I'll split the rest in smaller PRs.