Use group name instead of group.value as colunmName when there're only one group and one value selected
Display text labels for line, area chart
Set key, value automatically when data is updated and no previously selected key, value columns are valid
When no keys, groups but values are selected, handle it proper way
Handle some exceptional case
Add missing semicolon
Merge pull request #185 from NFLabs/pivot_improve

Improve graph / pivot behavior