home: move clear history to settings

This patch moves the "clear history" button to the settings page, in
a new "privacy" category.
The home actionbar is cleaned and the "Scan QR Code" action has now
its own button with a new image.

Change-Id: I29407bdbdebcf0610920c465d422da721479ed96
Tuleap: #646
diff --git a/ring-android/app/src/main/res/values/strings_preferences.xml b/ring-android/app/src/main/res/values/strings_preferences.xml
index 5ba5c81..0b6a545 100644
--- a/ring-android/app/src/main/res/values/strings_preferences.xml
+++ b/ring-android/app/src/main/res/values/strings_preferences.xml
@@ -3,6 +3,7 @@
     <string name="pref_category_network">Network</string>
     <string name="pref_category_contacts">Contacts</string>
     <string name="pref_category_system">System</string>
+    <string name="pref_category_privacy">Privacy</string>
 
     <string name="pref_mobileData_key" translatable="false">pref_mobileData</string>
     <string name="pref_mobileData_title">Mobile data</string>
@@ -23,4 +24,9 @@
     <string name="pref_startOnBoot_key" translatable="false">pref_startOnBoot</string>
     <string name="pref_startOnBoot_title">Start Ring on startup</string>
     <string name="pref_startOnBoot_summary">Run Ring in the background when the system starts.</string>
+
+    <string name="pref_clearHistory_key" translatable="false">pref_clearHistory</string>
+    <string name="pref_clearHistory_title">Clear history</string>
+    <string name="pref_clearHistory_summary">Clear all the conversations history. This action can not be undone.</string>
+
 </resources>