briar-headless: Address second round of review comments

briar-headless/README.md

...main/java/org/briarproject/briar/headless/BriarService.kt

...in/java/org/briarproject/briar/headless/HeadlessModule.kt

...s/src/main/java/org/briarproject/briar/headless/Router.kt

...a/org/briarproject/briar/headless/blogs/BlogController.kt

...g/briarproject/briar/headless/blogs/BlogControllerImpl.kt

...g/briarproject/briar/headless/blogs/HeadlessBlogModule.kt

.../briarproject/briar/headless/contact/ContactController.kt

...arproject/briar/headless/contact/ContactControllerImpl.kt

...arproject/briar/headless/contact/HeadlessContactModule.kt

.../briarproject/briar/headless/event/HeadlessEventModule.kt

.../briarproject/briar/headless/event/WebSocketController.kt

...arproject/briar/headless/event/WebSocketControllerImpl.kt

...org/briarproject/briar/headless/forums/ForumController.kt

...briarproject/briar/headless/forums/ForumControllerImpl.kt

...briarproject/briar/headless/forums/HeadlessForumModule.kt

...oject/briar/headless/messaging/HeadlessMessagingModule.kt

...oject/briar/headless/messaging/MessagingControllerImpl.kt

...rproject/briar/headless/messaging/OutputPrivateMessage.kt

...g/briarproject/briar/headless/blogs/BlogControllerTest.kt