Added support for scheme management (#1142)

* wip

* Added scheme management metadata properties to TargetScheme

* wip

* Added Scheme.Management for metadata

* use sharedDefault

* move generateSchemeManagement to SchemeGenerator

* revert

* update changelog

* update docs

* update test case

* remove

* remove unused file

* revert

* changed on fixtures project

* Updated ProjectSpec docs index

* User Scheme.Management also for TargetSchemes, use XCUserData

* Changelog

* Switch XcodeProj back tuist/XcodeProj - 8.9.0

* Reindent TOC Docs/ProjectSpec.md

* Revert swift tools version

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Co-authored-by: Tieme van Veen <tiemevanveen@hotmail.com>