Refactored the MessageMetadataRegistry class. Facilitated to remove the un-necessary warning which is displayed when a 3.x endpoint publishes an event which is an interface, where the 3.x endpoint added an __impl to the event type in the header. Relates to #1834
Fixed the variable names for metadata. Relates to #1834
Improved exception message that AssemblyScanner outputs
Ensuring that if EndpointConfigurationType is specified no scanning is performed by host
Added flag to AssemblyScanner to not throw exceptions.

This is to be used by the NSB host so that the initial scanning does not throw and prevent the whole endpoint from starting.
Exposed a flag to show whether there were errors during scanning
Merge remote-tracking branch 'origin/develop' into AssemblyScanner
Merge branch 'develop' into AssemblyScanner
Merge branch 'AssemblyScanner' into develop
Merge remote-tracking branch 'origin/issue-1834' into develop
Marked InMemory as obsolete, closes #1983