Fixed #58.

Initial attempt to fix this issue,

1. When assemblies are being registered, find PCL ones and add their profile paths to search paths.
2. Suppress `CopySecurityDeclarations` exceptions as PCL ones do not have security declarations.

Both changes are experimental as I only run through initial testing on simple cases.
What kind of exceptions can occur here and need to be ignored ? I tend to prefer checks over thrown/ignored exceptions when possible, not sure if it's feasible here.