conversation: delete individually

This patch introduces the ability to delete a conversation individual-
ly. This can be performed in each opened conversation.
The process deletes all the textmessages and calls histories from the
database.
A conversation refresh is done afterwards to rebuild the data states.

Change-Id: I3366de089a505bfd76196f7c90a4b8db453c0912
Tuleap: #629
diff --git a/ring-android/app/src/main/res/values/strings.xml b/ring-android/app/src/main/res/values/strings.xml
index 076d501..d0e5227 100644
--- a/ring-android/app/src/main/res/values/strings.xml
+++ b/ring-android/app/src/main/res/values/strings.xml
@@ -151,4 +151,9 @@
     <string name="clear_history_dialog_message">This action can not be undone.</string>
     <string name="clear_history_completed">History has been cleared.</string>
 
+    <!-- Conversation -->
+    <string name="conversation_action_delete_this">Delete this conversation</string>
+    <string name="conversation_action_delete_this_title">Delete this conversation ?</string>
+    <string name="conversation_action_delete_this_message">This action can not be undone.</string>
+
 </resources>