The ornamental design for a storagecontainer, as shown and described.
FIG. 1 is a perspective view of an embodiment of a storage container of our new design.
FIG. 2 is a front view thereof.
FIG. 3 is a left side view thereof; and,
FIG. 4 is a right side view thereof.
The back and bottom of the storage container are not part of our claimed design. The broken lines depict environmental subject matter only and form no part of the claimed design.