The ornamental design for a towelholder, as shown and described.
FIG. 1 is a perspective view of a towel holder showing an embodiment of my design with different cutout images on each side.
FIG. 2 is a front side view of the towel holder of FIG. 1 with the rear side view being a mirror image of the front side view.
FIG. 3 is a top view of the towel holder of FIG. 1.
FIG. 4 is a bottom view of the towel holder of FIG. 1.
FIG. 5 is a right side view of the towel holder of FIG. 1.
FIG. 6 is a left side view of the towel holder of FIG. 1.
FIG. 7 is a perspective view of a towel holder showing an embodiment of my design with the right side cutout images being the same as the left side cutout images; and,
FIG. 8 is a perspective view of a towel holder showing an embodiment of my design with the right side having cutout images and the left side not having cutout images.
The broken line showing in the figures is included for the purpose of illustrating portions of the towel holder and form no part of the claimed design.