Show a status screen when opening the database or applying migrations

...va/org/briarproject/bramble/api/db/DatabaseComponent.java

...g/briarproject/bramble/api/db/DatabaseMigrationEvent.java

...va/org/briarproject/bramble/api/db/MigrationListener.java

.../briarproject/bramble/api/lifecycle/LifecycleManager.java

...riarproject/bramble/api/lifecycle/event/StartupEvent.java

...e/src/main/java/org/briarproject/bramble/db/Database.java

...va/org/briarproject/bramble/db/DatabaseComponentImpl.java

...src/main/java/org/briarproject/bramble/db/H2Database.java

...in/java/org/briarproject/bramble/db/HyperSqlDatabase.java

...c/main/java/org/briarproject/bramble/db/JdbcDatabase.java

.../briarproject/bramble/lifecycle/LifecycleManagerImpl.java

...rg/briarproject/bramble/db/DatabaseComponentImplTest.java

...va/org/briarproject/bramble/db/DatabaseMigrationTest.java

...project/bramble/db/DatabasePerformanceComparisonTest.java

...t/java/org/briarproject/bramble/db/DatabaseTraceTest.java

...st/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

...riarproject/bramble/db/SingleDatabasePerformanceTest.java

...va/org/briarproject/bramble/test/TestLifecycleModule.java

briar-android/src/main/AndroidManifest.xml

...ain/java/org/briarproject/briar/android/BriarService.java