Add signing options to CMake/iOS build configuration

Adds the signing settings to iOS configurations.
Adds placeholders for signing flags to the initial CMake arguments, and
updates the CMake configuration when signing settings change.

The new configuration doesn't get automatically applied. Only the "Apply
Configuration Changes" button gets enabled and the user has to press
that explicitly. This seems to be a more general issue affecting the QML
debugging setting too, though.

Task-number: QTCREATORBUG-23574
Change-Id: I3e8d45f565347e1ad2ac274a21b1552f1510e8f4
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/ios/iosplugin.cpp

@@ -69,7 +69,8 @@ public:
 class IosPluginPrivate
 {
 public:
-    IosBuildConfigurationFactory buildConfigurationFactory;
+    IosQmakeBuildConfigurationFactory qmakeBuildConfigurationFactory;
+    IosCMakeBuildConfigurationFactory cmakeBuildConfigurationFactory;
     IosToolChainFactory toolChainFactory;
     IosRunConfigurationFactory runConfigurationFactory;
     IosSettingsPage settingsPage;