[TDF] Add the GetColumnNames method to the TInterface
[TDF] Add the GetColumnNames method to the TInterface

to give the possibility to the user to get the column names from the
TDataFrame nodes.

olifre/root,olifre/root,olifre/root,root-mirror/root,zzxuanyuan/root,olifre/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,zzxuanyuan/root,karies/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,karies/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,olifre/root,karies/root,zzxuanyuan/root,olifre/root,zzxuanyuan/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,zzxuanyuan/root,zzxuanyuan/root,karies/root,olifre/root,zzxuanyuan/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,zzxuanyuan/root,karies/root