Added support for objects which override the ToString method in SessionModelConverter

SessionModelConverter only had support for types marked as Serializable.
With this change, it also checks if the type has overridden the ToString
method in which case it calls it. If the type is neither marked as
serializable nor has the ToString method, then the "Non serializable
type" error message is shown in the Session tab.
Added unit tests for SessionModelConverter
Fixed and refactored SessionModelConverter unit tests

Some incorrect Assert's were fixed.
Fixed whitespaces in last commit
Merge branch 'master' of https://github.com/vape/Glimpse

Conflicts:
	source/Glimpse.Test.AspNet/SerializationConverter/SessionModelConverterShould.cs
Merge pull request #327 from vape/master

Added support for objects which override the ToString method in SessionModelConverter