Android Tests: Fix `BaseballCardSQLHelperTest`

Change `BaseballCardSQLHelperTest` to extend `InstrumentationTestCase`
rather than `AndroidTestCase`. This is necessary in order to access the
resources `assets` folder of the `bbct-common-tests` project.
Android Tests: Fix database creation for testing

The `DatabaseUtil` constructor now attempts to create the database if it
does not exist before opening it. This ensures that the
`BaseballCardList` activity will have data available when it first
starts.