[android] only enable image feature if contact supports it

Also show an onboarding the first time, the feature gets activiated

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

@@ -0,0 +1,11 @@
+<vector
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	android:width="24dp"
+	android:height="24dp"
+	android:alpha="0.56"
+	android:viewportHeight="24"
+	android:viewportWidth="24">
+	<path
+		android:fillColor="#000"
+		android:pathData="M2.28,3L1,4.27L3,6.27V19A2,2 0 0,0 5,21H17.73L19.73,23L21,21.72L2.28,3M4.83,3L21,19.17V5C21,3.89 20.1,3 19,3H4.83M8.5,13.5L11,16.5L12,15.25L14.73,18H5L8.5,13.5Z"/>
+</vector>

briar-android/src/main/res/layout/text_input_view.xml

@@ -40,7 +40,7 @@
 				android:focusable="true"
 				android:padding="4dp"
 				android:scaleType="center"
-				android:src="@drawable/ic_image"
+				android:src="@drawable/ic_image_off"
 				android:visibility="invisible"
 				app:tint="?attr/colorControlNormal"/>
 

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

@@ -144,6 +144,10 @@
 	<string name="dialog_message_save_image">Saving this image will allow other apps to access it.\n\nAre you sure you want to save?</string>
 	<string name="save_image_success">Image was saved</string>
 	<string name="save_image_error">Could not save image</string>
+	<string name="dialog_title_no_image_support">Images Unavailable</string>
+	<string name="dialog_message_no_image_support">Your contact\'s Briar does not yet support image attachments. Once they upgrade you\'ll see a different icon.</string>
+	<string name="dialog_title_image_support">You can now send images to this contact</string>
+	<string name="dialog_message_image_support">Tap this icon to attach images.</string>
 
 	<!-- Adding Contacts -->
 	<string name="add_contact_title">Add a Contact</string>