Made Glimpse NuGet package discovery more stable

When there are assemblies in the application's run directory that give
an exception when requesting custom attributes, the whole glimpse.axd
page crashed. This fix will list those "bad" assemblies and prevent the
glimpse.axd from crashing
Renamed NuGet package discovery classes

Since they are not Glimpse specific but are actually intended to
discover NuGet packages. The idea is to have the NuGetPackageAttribute
moved to NuGet eventually.
Aligned NuGetPackageAttribute values

- An explicit value of Glimpse for the Core projecten (otherwise we
would get Glimpse.Core as package name)
- An explicit value for the "normal/base" projects
- No value (so that it will be determined based on the assembly at
runtime) for the .NET framework version specific projects
Merge pull request #496 from Glimpse/GlimpseNuGetPackageDiscovery

Made Glimpse NuGet package discovery more stable, this will fix issue #477