lineage-sdk: Add kill app back button configs and strings

Change-Id: I867de293fc6e160a86a64d96035704d82b270f4e

lineage/res/res/values/config.xml

@@ -236,4 +236,8 @@
     <!-- Indicates that the device has Single-stage Camera key
          (without "Focus" state) instead of Dual-stage. -->
     <bool name="config_singleStageCameraKey">false</bool>
+
+    <!-- Timeout in MS for how long you have to long-press the back key to
+         kill the foreground app. -->
+    <integer name="config_backKillTimeout">2000</integer>
 </resources>

lineage/res/res/values/strings.xml

@@ -205,4 +205,7 @@
 
     <!-- General purpose use "unknown" string -->
     <string name="unknown">Unknown</string>
+
+    <!-- Long-press back kill application -->
+    <string name="app_killed_message">Application killed</string>
 </resources>

lineage/res/res/values/symbols.xml

@@ -147,4 +147,8 @@
     <!-- Last app switch animations -->
     <java-symbol type="anim" name="last_app_in" />
     <java-symbol type="anim" name="last_app_out" />
+
+    <!-- Back kill -->
+    <java-symbol type="string" name="app_killed_message" />
+    <java-symbol type="integer" name="config_backKillTimeout" />
 </resources>