Consistent CamelCasing for Application and Module

Default module = 'Core', and application = 'Backend' or 'Frontend'
Changelog backend_ajax was correct

Since this is an old part of the changelog, backend_ajax was still
correct.
'core' should be 'Core' in backend locale model
Merge pull request #706 from jeroendesloovere/3.7-wip-ExceptionHandling

Consistent CamelCasing for Application and Module