Created attachment 75767 [details]
Example spreadsheet to test this

Problem description: 
It is currently impossible to format text in text boxes that are part of a chart in Calc.
However, text formatting is possible in boxes created in the rest of the spreadsheet.

Steps to reproduce:
1. Create a chart in a .ods document
2. Add a title (axis or main)
3. Try to format a section of the text (subscript, superscript, bold, italic...)

Current behavior:
Even though it is possible to format the whole title (bold, italic, bold and italic, font and font size), there are no options for formatting a portion of text.

Expected behavior:
There should be at least basic options to format a section of text, as this would be helpful in many cases, e.g. superscript numbers for functions or subscript numbers for chemicals.
Operating System: Ubuntu
Version: 3.6.5.2 release