Add recently connected state to core and UI.

...g/briarproject/bramble/api/plugin/ConnectionRegistry.java

...org/briarproject/bramble/api/plugin/ConnectionStatus.java

...ramble/api/plugin/event/ConnectionStatusChangedEvent.java

...ct/bramble/api/plugin/event/ContactDisconnectedEvent.java

...g/briarproject/bramble/plugin/ConnectionRegistryImpl.java

...iarproject/bramble/plugin/ConnectionRegistryImplTest.java

...a/org/briarproject/briar/android/contact/ContactItem.java

...rproject/briar/android/contact/ContactItemViewHolder.java

...riarproject/briar/android/contact/ContactListAdapter.java

...iarproject/briar/android/contact/ContactListFragment.java

...g/briarproject/briar/android/contact/ContactListItem.java

...ject/briar/android/contact/ContactListItemViewHolder.java

...oject/briar/android/controller/SharingControllerImpl.java

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

...ct/briar/android/introduction/ContactChooserFragment.java

...roid/privategroup/memberlist/GroupMemberListActivity.java

...rivategroup/memberlist/GroupMemberListControllerImpl.java

...ar/android/privategroup/memberlist/MemberListAdapter.java

...briar/android/privategroup/memberlist/MemberListItem.java

...android/privategroup/memberlist/MemberListItemHolder.java