Initial version of Lavision Imspector reader

Metadata population still needs work, as does support for larger stacks.

See ticket #8071.
Update Imspector reader to support larger datasets
Force stricter type checking

There are multiple formats with the .msr extension, so suffix checking
is not sufficient.
Remove unnecessary 'if' statement
Prevent invalid offsets and block sizes from being used
Better original metadata value parsing
Minor code cleanup and addition of comments
Merge pull request #620 from melissalinkert/imspector

Add support for Lavision Imspector data