The ornamental design for a towelcabinet, as shown and described.
FIG. 1 is a top, front and right side perspective view of a towel cabinet showing our new design;
FIG. 2 is a top plan view;
FIG. 3 is a left side elevational view;
FIG. 4 is a front elevational view;
FIG. 5 is a right side elevational view;
FIG. 6 is a rear elevational view, the broken line disclosure being understood to represent an unclaimed portion of the article in which the claimed design is embodied; and,