Fix EZP-20355: Insert table row in ezoe with embed elements

Description
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When inserting a new row in a table, the TinyMCE's table plugin (and thus eztable, our fork) tries to keep the formatting of the currently selected row. For instance, if a cell contains only a bold text, the corresponding cell in the new row will also get the HTML code to get its text in bold.

This feature does not play well with some of our tags used to structure content or inject higher level components like embed, the block custom tags or literal. This patch makes sure those custom elements are not cloned in a new cell even if the original cell has one of them.

(Note: the code is indented with tabs to keep consistency with the rest of the file)

Tests
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manual tests in IE[6-9], Firefox and Chrome.