Support build.xcconfig in /app/App_Resource/iOS folder

[ligaz]

It would be good if we pick up custom build.xcconfig file from the /app/App_Resource/iOS. This will allow developers to keep this file under source control without the need to modify it in the /platforms/ios.

[Mitko-Kerezov]

Related to #478

[PanayotCankov]

Then you can add to your project:

• app/App_Resources/iOS/Images.xcassets
• app/App_Resources/iOS/build.xcconfig

And use icons and launch images from the xccassets by setting the following flags in the build.xcconfig:

ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = Brand Assets;