Merge branch 'illustration-revamp' into 'master'

briar-android/artwork/bluetooth.svg

briar-android/artwork/empty_state_blog.svg

briar-android/artwork/empty_state_contact_list.svg

briar-android/artwork/empty_state_forum_list.svg

briar-android/artwork/empty_state_group_list.svg

briar-android/artwork/ic_check_circle_dark.svg

briar-android/artwork/ic_check_circle_light.svg

briar-android/artwork/ic_error.svg

briar-android/artwork/ic_exclamation_mark.svg

briar-android/artwork/il_add_contact_remote_dark.svg

briar-android/artwork/il_add_contact_remote_light.svg

...r-android/artwork/il_add_contact_remote_nickname_dark.svg

...-android/artwork/il_add_contact_remote_nickname_light.svg

briar-android/artwork/il_bluetooth_connect_dark.svg

briar-android/artwork/il_bluetooth_connect_light.svg

briar-android/artwork/il_crash_dark.svg

briar-android/artwork/il_crash_light.svg

briar-android/artwork/il_empty_state_blogs_dark.svg

briar-android/artwork/il_empty_state_blogs_light.svg

briar-android/artwork/il_empty_state_contact_list_dark.svg