Add escapeReservedKeywords in all templates where needed

[djbe]

Fixes #3.

Only the structured/dot-syntax string templates already had this. In some places in the storyboards templates, it isn't needed to escape the identifier because "Scene" or "ViewController" is appended to it.

[AliSoftware]

We should add unit tests for that.
I mean, not really add, but just change the current fixtures so they all have at least one asset named with a reserved, and adapt the expected output to ensure it's properly escaped (and then #15 and #16 would help ensure it's valid Swift)