resourceloader: Also clear store in debug mode to simplify mw.loader.store.init()

resourceloader: Also clear store in debug mode to simplify mw.loader.store.init()

This makes it consistent with the other two circumstances in which
mw.loader.store is disabled.

Also, it makes debug=true a more easily accessible means for users
to clear module storage, which can be useful at times (without requiring
console access).

Change-Id: I9c66815a2f6c60feef3e070cfe57c382a69cc752