Attempt at disbling grace period in response to issue #3114 (#3116)

src/main/res/values/arrays.xml

@@ -73,12 +73,14 @@
 	</string-array>
 
 	<string-array name="grace_periods">
+		<item>@string/gp_disable</item>
 		<item>@string/gp_short</item>
 		<item>@string/gp_medium</item>
 		<item>@string/gp_long</item>
 	</string-array>
 
 	<string-array name="grace_periods_values">
+		<item>0</item>
 		<item>144</item>
 		<item>610</item>
 		<item>2584</item>

src/main/res/values/strings.xml

@@ -535,6 +535,7 @@
     <string name="choose_participants">Choose participants</string>
     <string name="creating_conference">Creating group chat…</string>
     <string name="invite_again">Invite again</string>
+    <string name="gp_disable">Disable</string>
     <string name="gp_short">Short</string>
     <string name="gp_medium">Medium</string>
     <string name="gp_long">Long</string>