Check for sheet name before adding. Fixes #378

Unknown changes - something to do with line endings?

Parse commas in print area (#263) ...

* add method to format the defined names if a comma exists in the sheet name

* add Excel workbook to test loading of sheets with commas in them (when they have a print area)

* Regex change to make sure all tests pass successfully

* use String.Format instead of new fangled string interpolation.

* Improve defined name parsing.

* Add unit test for references to a sheet with commas in the name

* Add unit tests and adjust CalcEngine to allow enclosing characters around identifiers

* Reformat code using CodeMaid

* Don't use C#6 syntax for dictionary initialiser.

Project hierarchy cleanup