doctrine filter to remove embedded blocks when editing rendered content

[dbu]

f.e. in frontend editing, the cmf_block_embed filter might have rendered blocks that get stored as rendered blocks on a save. we should have the filter output some special token to detect that this was content it generated and create a doctrine listener that on saving removes the generated stuff again and restores the call.
something like

....

(if the frontend editor goes destroying that something while editing, then screw him).

this concept could be applied to any filter thing somebody comes up with: if you provide a filter, you should provide a listener as well. each filter you activate is going to cost you. listening on save operations should be comparably cheap as its not happening that often. and anyway is not more expensive than rendering the page.

[dbu]

there is a discussion about making this a more general cmf feature: symfony-cmf/routing-bundle#178