Make Kiwi spec file template work with category names

I noticed using the Kiwi spec Xcode file template that if you enter a category name for the file under test (eg. "MyObject+Extra" that it converts this to an identifier in the file template, and replaces + with _. I think this may be necessary with SenTestCase/XCTestCase subclasses, but isn't necessary for Kiwi, as long as the class specified in `SPEC_BEGIN` has been converted to a valid class name.

This might be a matter of personal preference, I'm not sure what everyone else does in this case. I usually have `MyObject+Extras.m` and `MyObject+ExtrasSpec.m`.

Removing the `:identifier` from the template info and the base template file means adding categories works as I would have expected. The underlying Kiwi class name generated from SPEC_BEGIN will still convert to `MyObject_ExtrasSpec`.

Are there other cases where converting to an identifier is necessary for the file name itself?