Providing more detailed instructions for adding contacts

Users were confused by the process of adding a contact for the first time.
This change adds additional explanation and a picture of what is going on.

It also moves part of the UI into XML files.

Closes #87

briar-android/res/layout/invitation_bluetooth_start.xml

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              android:orientation="vertical"
+              android:layout_width="match_parent"
+              android:layout_height="match_parent"
+              android:padding="7dp">
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/your_nickname"
+        android:id="@+id/yourNicknameView"
+        android:padding="7dp"/>
+
+    <Spinner
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:id="@+id/spinner"
+        android:spinnerMode="dropdown"
+        android:padding="7dp"/>
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/face_to_face"
+        android:id="@+id/faceToFaceView"
+        android:padding="7dp"/>
+
+    <ImageView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:id="@+id/imageView"
+        android:src="@drawable/bluetooth"
+        android:scaleType="fitCenter"
+        android:baselineAlignBottom="false"
+        android:cropToPadding="false"
+        android:layout_weight="1"/>
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/bluetooth_explanation"
+        android:id="@+id/explanationView"
+        android:padding="7dp"/>
+
+    <Button
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="@string/continue_button"
+        android:id="@+id/continueButton"
+        android:layout_gravity="center_horizontal"
+        android:layout_weight="0"/>
+</LinearLayout>

briar-android/res/values/strings.xml

@@ -36,8 +36,9 @@
     <string name="contact_list_title">Contacts</string>
     <string name="no_contacts">No contacts</string>
     <string name="add_contact_title">Add a Contact</string>
-    <string name="your_nickname">Your nickname: </string>
+    <string name="your_nickname">Please select the identity you want to use:</string>
     <string name="face_to_face">For security reasons you must be face-to-face with the person you want to add as a contact.\n\nThis will prevent anyone from impersonating you or reading your messages in future.</string>
+    <string name="bluetooth_explanation">Contacts need to add each other at the same time. Please continue together and allow Bluetooth to be enabled for the process to work.</string>
     <string name="continue_button">Continue</string>
     <string name="your_invitation_code">Your invitation code is</string>
     <string name="enter_invitation_code">Please enter your contact\'s invitation code:</string>