The ornamental design for a columnsupport, as shown and described.
FIG. 1 is a perspective view of a column support according to my design;
FIG. 2 is a plan view thereof; and,
FIG. 3 is a side view thereof.
Throughout the various figures of the drawings, certain views may not be provided. The omission of a particular view is intended to convey that the element(s) depicted is/are plain and unornamented in that omitted view, or that the particular ornamental appearance in that view is simply not claimed.