[DRAFT] convenience class for dealing with ODF styling information.

The class parses the styling information and allows accessing it like e.g.
 fontWeight = style.getTextStyle("T1").text.fontWeight;
If T1 does not define, fontWeight is retrieved from the parent style and
eventually the document default and the implementation default.
This is achieved by setting the object prototype to the style parent.
Parsing of styles is done lazily (when getStyle()) is called.
When the styling information, changes, this class needs to be invalidated, so the information is parsed again when accessed.

This does not yet properly implement the description at
 http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1416272_253892949
and it cannot with current API in the draft class. The call getTextStyle() should accept an ODF element. Then *:style-name, *:class-names and the element hierarchy should be taken into account.

In order to be able to use this class to generate css and to make the amount of parsing code small, a configuration object that maps js properties to xml values should be added. This configuration then also lists a function that converts the xml/js value to css values. It also lists the function that parses the xml value to the js value.