Shoobx.rml2odt

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- Complete overhaul of blockTable styling.
This enables the use blockTableStyle and `td` styling tags.
Most text, background and border styling is supported.

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- Fix: `img` must be in a Paragraph otherwise LibreOffice will not show the
Image

- Code cleanup and refactor

- Lots of fixes, cleanup, tests added

- Fix: blockSpan handling was completely broken

- Fix: Removed whitespace from `para` left text,
removed tail text of `para` tag

- Fix: `NextPage` did not work, it added no page break

- Fix: Do not add tabs to the ODT output, reportlab does not either.
There's a special `tab` tag that is used by our custom numbering.

- Fix: Do not fail on missing `value` of the `color` tag

- Fix: Support `pre` and `xpre` tags, make sure whitespace is not squashed

- Fix: Copy the `main` or `Main` pageTemplate to `Standard` to make ODT
at least somehow happy. Reportlab uses `main` as conventional default.
This is still just a workaround. Supporting custom templates set in a story
will take more efforts.

- Copied all z3c.rml RML test inputs, blacklisted a lot, listed shortcomings.

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- Fix: Next paragraph text strip for custom bullets broken by 0.4.3.

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- Fix: bullet numbering ignored `value` as start

- Fix: support all custom `li` bullets (l, L, o, O, r, R)

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- Fix: the `br` tag used a class variable to remember whether it added the
style `BreakJustify`.
- Fix `span` tag handling. It literally discarded most text.

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- Fix: Text following a comment tag was discarded.

- Fix: 3+ whitespace was replaced with nothing. Caused text to miss spaces.