Additional ScanModes in AssemblyTypeScanner

Added additional ScanModes: 
OnlyNancyNamespace
ExcludeNancyNamespace

These will check for types with namespaces starting with "Nancy" instead of excluding whole assembly. This is to address the cases whereby the assembly are embedded in a bigger assembly
Yes I can if this is agreeable by the original writer. 

It was originally written as if/else statements which I find to be odd syntactical but have chosen to follow the convention