change the default root name. Use CFBundleExecutable instead of CFBundleDisplayName.

CFBundleDisplayName is localizable.
If I added a localized file, the root name is localized.
Then the app will be missing the database file.
Merge pull request #31 from katsuyoshi/db_name

change the default root name. Use CFBundleExecutable instead of CFBundleDisplayName.