implement call duration display with NewCallModel

This NSTextField was hidden as it wasn't reimplemented during the
NewCallModel refactoring in CurrentCallVC. It is now working as
expected by asking the model once per second for the new duration
value.

Change-Id: I27bd8f578ce5010e9311938f71ca610197f7357b
Reviewed-by: Kateryna Kostiuk <kateryna.kostiuk@savoirfairelinux.com>
diff --git a/ui/Base.lproj/CurrentCall.xib b/ui/Base.lproj/CurrentCall.xib
index 5b3cade..84817ad 100644
--- a/ui/Base.lproj/CurrentCall.xib
+++ b/ui/Base.lproj/CurrentCall.xib
@@ -56,7 +56,7 @@
                                 <customView translatesAutoresizingMaskIntoConstraints="NO" id="d0X-cW-Xgz">
                                     <rect key="frame" x="20" y="438" width="705" height="71"/>
                                     <subviews>
-                                        <textField hidden="YES" horizontalHuggingPriority="251" verticalHuggingPriority="750" allowsCharacterPickerTouchBarItem="YES" translatesAutoresizingMaskIntoConstraints="NO" id="cIU-M7-xpN">
+                                        <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" allowsCharacterPickerTouchBarItem="YES" translatesAutoresizingMaskIntoConstraints="NO" id="cIU-M7-xpN">
                                             <rect key="frame" x="583" y="23" width="104" height="24"/>
                                             <constraints>
                                                 <constraint firstAttribute="width" constant="100" id="9vz-kb-6L6"/>