Support for new portable profile 7 (#204) (WIP)
Fix portable profile 7 problems (closes #281)

*Use Assembly.LoadFrom on all FSharp.Core versions and profile 47 system assemblies (things with version 2.0.5.0)
*Use Assembly.Load on full .NET and on profile 7 system assemblies
Signature tests for profile 7
Fix tests
Merge pull request #281 from ovatsus/Profile7

Support for new portable profile 7 (WIP)