libmsooxml: libmsooxml: fine tuned text:line-break processing

Introducing a new <text:span> element having text-properties
defined by endParaRPr in selected situations in order to prevent
usage of the styleForModification function:

* Do not save text-properties into paragraph styles also in case
of empty paragraphs. Save an empty <text:span> having
text-properties defined by endParaRPr. Looking for the default
font size defined by the application in case the endParaRPr
formatted span is removed and new text is inserted.

* Insert an empty <text:span> having text-properties defined by
endParaRPr in case the <text:line-break> is the last element of
the paragraph in order to apply the correct fo:font-size to the
new line. Replaced the original fo:font-size from
text-properties of <text:line-break> by TEXT_FONTSIZE_MIN to
not affect the line-height calculation of both the new line and
the current line. This disables of course application of the
default font-size defined by the application in case of
<text:line-break>.

* Removing the fo:text-transform attribute is also removed from
text-properties of text:line-break because it disables its
functionality during layout (did not check the layout part).

* Also removing the style:text-underline-style attribute. If
text styles of the text chunk and text:line-break match,
underline is applied until end of the line during layout.