Show Blog Invitations

This refactors the forum invitation code,
so it can be used by both: forums and blogs.

briar-android/res/layout/activity_invitations.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <org.briarproject.android.util.BriarRecyclerView
-	android:id="@+id/availableForumsView"
+	android:id="@+id/invitationsView"
 	xmlns:android="http://schemas.android.com/apk/res/android"
 	android:layout_width="match_parent"
 	android:layout_height="match_parent"/>

briar-android/res/values/strings.xml

@@ -316,6 +316,10 @@
 	<string name="blogs_sharing_invitation_received">%1$s has shared the personal blog of %2$s with you.</string>
 	<string name="blogs_sharing_invitation_sent">You have shared the personal blog of %1$s with %2$s.</string>
 	<string name="blogs_sharing_show_invitations">Show Blog Invitations</string>
+	<string name="blogs_sharing_invitations_title">Blog Invitations</string>
+	<string name="blogs_sharing_exists">You are subscribed to this blog already.\nWarning: Accepting again might reveal that %s is your contact.</string>
+	<string name="blogs_sharing_joined_toast">Subscribed to Blog</string>
+	<string name="blogs_sharing_declined_toast">Blog Invitation Declined</string>
 
 	<string name="blogs_blog_list">Blog List</string>
 	<string name="blogs_available_blogs">Available Blogs</string>