Merge branch '594-db-migrations' into 'master'

.../org/briarproject/bramble/api/db/DataTooNewException.java

.../org/briarproject/bramble/api/db/DataTooOldException.java

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

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

...n/java/org/briarproject/bramble/db/DatabaseConstants.java

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

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

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

...est/java/org/briarproject/bramble/db/H2MigrationTest.java

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