Changes:
* Condense Routing.sln into HttpAbstractions.sln
* Workaround NU1105 by adding all ProjectReferences to the .sln
* Workaround exceptions in the ReferencesHostBridge by moving Reference items to a temporary item group
* Add a 'startvs.cmd' script for launching VS with the right env variables
* Remove RangeHelper test project
* Move RangeHelper tests into StaticFiles.Tests and add target for NPM restore
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