Revert "Rename VolcanoApplication to VolcanoApplication.java"

This reverts commit 4e3c54d4bd4f821e1ca2066c02da3efc44e28b9d.
Revert "Revert "Rename VolcanoApplication to VolcanoApplication.java""

This reverts commit 6cf13e33eb3afb122d5cac319e92538d04abbe2e.