Revert "Revert "Make reference a string with the limitation that it cannot contain invalid filename chars.""

This reverts commit 64d888533b3432e9ed4db524cae3754337ab1c5d.
Added test for ArgumentException when reference contains invalid filename chars.
Revert "Revert "Make reference a string with the limitation that it cannot contain invalid filename chars.""

This reverts commit 64d888533b3432e9ed4db524cae3754337ab1c5d.
Added test for ArgumentException when reference contains invalid filename chars.
Updated UrlHelperExtensions with string reference instead of Guid.
Merge branch 'make-reference-string' of https://github.com/mwijnands/PluploadMvc.git
Merge pull request #8 from mwijnands/make-reference-string

Make reference a string. Solves #5.