use the default ScriptMetadataResolver for scripts

[filipw]

Fixes #702.

This allows OmniSharp to support intellisense when GAC reference is used. i.e. instead of:

#r "C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6\System.Web.dll"

we can use:

#r "System.Web"

This is in line with the default CSI behavior, which supports GAC references.

[filipw]

in action:

[filipw]

thanks - let's punch this in then!