Merge branch 'origin/master'
store category type and categories (or borders, with numeral values)
move add categorie functionality to function (so that it can be called from "outside")
remember type and categories of piechart (if they are defined)
add edit button to piecharts
keep chart data (all distinct values) in function, for better access
code cleanup: call dialog creation functions from "constructor"
make text-based piecharts editable
make numeral-based piecharts editable
Merge branch 'piechart'