[android] Swipe left/right in image screen to see other images from the same message

...riarproject/briar/android/activity/ActivityComponent.java

...iarproject/briar/android/conversation/AttachmentItem.java

...ject/briar/android/conversation/ConversationActivity.java

...riarproject/briar/android/conversation/ImageActivity.java

...riarproject/briar/android/conversation/ImageFragment.java

...iarproject/briar/android/conversation/ImageViewModel.java

briar-android/src/main/res/layout/activity_image.xml

briar-android/src/main/res/layout/fragment_image.xml