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)
Good point about the link -- I'll change that.

About capitalization: I think of "Jump to Definition" and "Quick Edit" as sort of branded/proper names for specific features, while "code hints" is more of a generic term used in many products and not calling out a specific command or menu item.  But CC @njx & @dangoor for a second opinion :-)