Add support for several features for the RTF writer

[oleibman]

RTF Changes

1. Converter is currently expecting colors as strings of hex digits,
   but PhpWord allows specification of colors by named constant, so
   result is random when one of those is used. This change handles
   all the named colors.
2. Table needs \pard at end; formatting may be wrong without it.
3. RTF writer will no longer ignore paragraph style for TextRun.
4. RTF writer will no longer ignore paragraph and font style for Title.
5. Add support for RTF headers and footers.
6. Add support for right-to-left in font.
7. Add support for PageBreakBefore and LineHeight for paragraphs.
8. Add support for PageNumberingStart for sections.

There are test cases for all of these changes.

Fixes # (issue)

Checklist:

• I have run composer run-script check --timeout=0 and no errors were reported
• The new code is covered by unit tests (check build/coverage for coverage report)
• I have updated the documentation to describe the changes
  No documentation changes required.

[coveralls]

Coverage decreased (-0.1%) to 94.495% when pulling c52c7ab on oleibman:rtfchanges into 733f845 on PHPOffice:develop.

[oleibman]

I'm not sure if I need to do something about "resolve conflicts". Tests weren't working because fixes were required to AbstractWebServerEmbeddedTest.php, for which there was a pull request for a change which had not yet been merged, so I borrowed the code from that change. Now that it has been merged, it no longer needs to be part of this change, but I'm not sure how to disentangle it. Please let me know what I should be doing, if anything.

[troosan]

The best is to have a separate branch per implemented feature. You can of course have your own develop branch with everything merged.