The ornamental design for a cakecup, as shown and described.
FIG. 1 is a perspective view of a cake cup showing my new design;
FIG. 2 is a front perspective view thereof;
FIG. 3 is a top view thereof; and,
FIG. 4 is a bottom view thereof.
The broken line showing of a straw and frosting feature is included for the purpose of illustrating environmental structure and forms no part of the claimed design.