[android] rough sketch of UI for adding contacts remotely

.../org/briarproject/bramble/api/contact/ContactManager.java

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

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

briar-android/artwork/ic_nearby.svg

briar-android/artwork/nickname.svg

briar-android/build.gradle

briar-android/src/main/AndroidManifest.xml

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

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

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

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

...riar/android/contact/add/remote/LinkExchangeFragment.java

...ct/briar/android/contact/add/remote/NicknameFragment.java

...r/android/contact/add/remote/PendingRequestsActivity.java

...ar/android/contact/add/remote/PendingRequestsAdapter.java

...android/contact/add/remote/PendingRequestsViewHolder.java

...briarproject/briar/android/viewmodel/ViewModelModule.java

briar-android/src/main/res/drawable/bubble_accent.xml

briar-android/src/main/res/drawable/bubble_completed.xml

briar-android/src/main/res/drawable/ic_call_made.xml