Merge branch '1643-controller-leaks' into 'master'

...a/org/briarproject/briar/android/blog/BaseController.java

...g/briarproject/briar/android/blog/BaseControllerImpl.java

...a/org/briarproject/briar/android/blog/BlogController.java

...g/briarproject/briar/android/blog/BlogControllerImpl.java

...ava/org/briarproject/briar/android/blog/BlogFragment.java

...org/briarproject/briar/android/blog/BlogPostFragment.java

...a/org/briarproject/briar/android/blog/FeedController.java

...g/briarproject/briar/android/blog/FeedControllerImpl.java

...ava/org/briarproject/briar/android/blog/FeedFragment.java

.../briar/android/privategroup/list/GroupListController.java

...ar/android/privategroup/list/GroupListControllerImpl.java

...ct/briar/android/privategroup/list/GroupListFragment.java