BasicPersistence: move the store to NSTemporaryDirectory() so we don't pollute the user's home directory without asking
ProjectDemo: AccountBox: Add warning that the password is stored in plaintext in NSUserDefaults
ProjectDemo: Move the default store location to ~/Library/CoreObjectProjectDemo/Store.coreobjectstore
Tests/Benchmark: move all testing stores to NSTemporaryDirectory to avoid cluttering the user's home directory.

The store URL is printed at the start of the test suite run in case it's needed for debugging.