Support new Unity build pipeline

[raldred]

Support the new Unity build pipeline using PostProcessBuildAttribute
Removed old shell scripts and implemented new c# script to automate adding of frameworks to xcode project using the new xcode tools provided by unity as part of the UnityEditor.iOS.Xcode namespace.

The old PostProcessBuildPlayer_GA & mod_pbxproj.py scripts are not longer necessary or supported.

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[raldred]

I signed it!

[googlebot]

CLAs look good, thanks!

[jjstaats]

The namespace UnityEditor.iOS.Xcode is define in "unityEditor.iOS.Extensions.xcode.dll" which is only installed when you also have IOSSupport playbackEngine installed. So you will want to add #if UNITY_IOS guards.

[raldred]

My apologies you're right. I will correct it asap.

[3ace]

I'm using Xcode 8.3.2 and latest iOS SDK.

Using this script, libz.dylib and libsqlite3.tbd would link to the wrong directory

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS10.3.sdk/System/Library/Frameworks

the correct path should be

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS10.3.sdk/usr/lib/

And libz.dylib no longer exist, replaced by libz.tbd.