String tweaks

Wanted to post this for discussion/review before the 0.44 string freeze hits.

* Empty pane message:
    - say "pane" instead of "view"
    - say "open" instead of "select" (to reduce the confusion in #9254)
* JS File Inference Problem dialog:
    - ask users to file a Brackets bug
    - fix capitalization
    - format more like other errors that call out a filename
* Remove unused UNSUPPORTED_FILETYPE error & its corresponding string (I think this was leftover from an earlier part of splitview)
Should link take user to [How to Report an Issue wiki page](https://github.com/adobe/brackets/wiki/How-to-Report-an-Issue) instead of directly to Issues page?