Bringing line and fill style of data labels to ODF

[Regina Henschel]

Hi NISZ LibreOffice Team, hi all,

I have started to bring the line and fill properties of data labels to 
ODF. Currently they are implemented in loext-Attributes in the styles of 
<chart:series> and <chart:data-point>. But ODF needs <chart:data-label> 
elements and have them as ordinary line and fill attribute in the data 
label styles.

My current state of work is in 
https://gerrit.libreoffice.org/c/core/+/102381.

Because you are heavily working on chart import/export, it might be 
useful, if you have a look, whether what I plan to do is in conflict 
with that, what you plan to do.

Kind regards
Regina