Implement contacts API

...n/java/org/briarproject/mailbox/android/MailboxService.kt

mailbox-cli/build.gradle

...org/briarproject/mailbox/core/contacts/ContactsManager.kt

...rc/main/java/org/briarproject/mailbox/core/db/Database.kt

...ain/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt

...main/java/org/briarproject/mailbox/core/server/Routing.kt

.../org/briarproject/mailbox/core/server/WebServerManager.kt

.../src/test/java/org/briarproject/mailbox/core/TestUtils.kt

...t/mailbox/core/contacts/ContactsManagerIntegrationTest.kt

.../contacts/ContactsManagerMalformedInputIntegrationTest.kt

...a/org/briarproject/mailbox/core/server/IntegrationTest.kt