Bug 833508 - Make GlobalSyncStage.{execute,resetLocal,wipeLocal} take GlobalSession argument.

Add AbstractSessionManagingSyncStage for managing GlobalSession parameter.
Bug 833508 - Remove GlobalSession argument to GlobalSyncStage constructors.
Bug 833508 - post: Remove FetchInfoCollectionsStage reference from TestGlobalSession.
Bug 833508 - post: Make MockAbstractNonRepositorySyncStage for rooting AbstractNonRepositorySyncStage test classes.
Bug 833508 - post: Add MockGlobalSession.withStage and use it in tests.
Bug 833508 - post: Delete RealPrefsMockGlobalSession.