Merge branch '1232-polling-events' into 'master'

...briarproject/bramble/api/contact/PendingContactState.java

...briarproject/bramble/api/rendezvous/RendezvousPoller.java

...ect/bramble/api/rendezvous/event/RendezvousPollEvent.java

.../org/briarproject/bramble/contact/ContactManagerImpl.java

...org/briarproject/bramble/rendezvous/RendezvousModule.java

...org/briarproject/bramble/rendezvous/RendezvousPoller.java

...briarproject/bramble/rendezvous/RendezvousPollerImpl.java

.../briarproject/bramble/contact/ContactManagerImplTest.java

...rproject/bramble/rendezvous/RendezvousPollerImplTest.java

.../briar/android/contact/add/remote/PendingContactItem.java

...ndroid/contact/add/remote/PendingContactListActivity.java

...droid/contact/add/remote/PendingContactListViewModel.java

.../android/contact/add/remote/PendingContactViewHolder.java

...rg/briarproject/briar/android/view/BriarRecyclerView.java

briar-android/src/main/res/values/strings.xml

briar-headless/README.md

...iarproject/briar/headless/contact/OutputPendingContact.kt