Use an in-memory database when running instrumented tests.

- added new TestRunner and new TestApplication
- The TestRunner loads TestApplication as the apps Application instance when running the tests
- added new interface AppConfig to retrieve the database name
- changed Startup (Application) so that it implements AppConfig
- changed CustomSQLiteOpenHelper so that it retrieves the database name from the Application instance
- Startup provides the production database name
- TestApplication provides null which yields an in-mememory database

src/main/java/de/dennisguse/opentracks/Startup.java

@@ -14,7 +14,7 @@ import de.dennisguse.opentracks.settings.PreferencesUtils;
  * NOTE: How often actual application startup happens depends on the OS.
  * Not every start of an activity will trigger this.
  */
-public class Startup extends Application {
+public class Startup extends Application implements AppConfig {
 
     private static final String TAG = Startup.class.getSimpleName();
 
@@ -40,4 +40,9 @@ public class Startup extends Application {
             StrictMode.enableDefaults();
         }
     }
+
+    @Override
+    public String getDatabaseName() {
+        return "database.db";
+    }
 }