Add CalDAV server strings

app/src/main/res/values/strings.xml

@@ -730,5 +730,8 @@ File %1$s contained %2$s.\n\n
   <string name="alarm_after_due">%s after due</string>
   <string name="snoozed_until">Snoozed until %s</string>
   <string name="custom_notification">Custom notification</string>
+  <string name="caldav_server_unknown">Unknown</string>
+  <string name="caldav_server_other">Other</string>
+  <string name="caldav_server_type">Server type</string>
   <string name="filter_snoozed">Snoozed</string>
 </resources>