Add api for writing ODF that is generated from the ODF RNG file.

Two years ago I wrote an initial version of this patch and a detailed discussion on the mailing list [1] followed. The main objections to the patch have been dealt with (see below).
Most of this new version was written at Akademy in Bilbao.

Very short summary of the patch:
This patch should help everybody, young and old, with coding C++ for writing ODF and make errors easier to catch.
The OpenDocument Format specification is published with a Relax NG file that specifies the XML format. This file can be used to check if ODF files are valid. It can also be used to generate a C++ API headers. This is what this patch does.

Example:
Instead of writing:
==
xmlWriter->startElement("text:p");
xmlWriter->addAttribute("text:style-name", "italic");
xmlWriter->startElement("text:p");
xmlWriter->addAttribute("text:style-name", "bold");
xmlWriter->addTextNode("Hello World!");
xmlWriter->endElement();
xmlWriter->endElement();
==
you can write:
==
text_p p(xmlWriter);
p.set_text_style_name("italic");
text_span span(p.add_text_span());
span.set_text_style_name("italic");
span.addTextNode("Hello World!");
==

Some advantages:
- autocompletion when coding: faster coding
- tag and attribute names are not strings but class and function names: less errors
- nesting is checked by the compiler
- you write to elements (span, p), not xmlwriter: easier to read
- required attributes are part of the element constructor

Implementation considerations:
- Calligra is large, so the generated code mixes well with the use of KoXmlWriter and porting can be done in small steps.
- class and function names are similar to the xml tags with ':' and '-' replaced by '_'.
- stack based: no heap allocations
- only header files: all code will inline and have low impact on runtime
- modular: one header file per namespace to reduce compile overhead
- code generator is Qt code, part of Calligra and runs as a build step

Not in this patch (and places where you can help in the future):
- generate enumerations based on Relax NG
- check data type for attributes (you can still write "hello" to an integer attribute)
- complete port of Calligra to the generated code
- improved speed by using static QString instead of const char*

Provided solutions to previously raised issues:
- modular headers to reduce compile overhead
- function "end()" to optionally close an element before it goes out of scope
- use structure of Relax NG file to reduce header sizes by inheritance from common groups
- provide most KoXmlWriter functionality safely through the element instances
- closing elements is now automatic at a slight runtime overhead