Remember files that timed out in Tern

This is a squashed version of PR https://github.com/adobe/brackets/pull/8198. See for more comments.

This is to finish Trello Card: https://trello.com/c/2ra9FzGL/1284-m-js-code-hints-automatic-crash-preventer
What I was thinking was that there's just one exclusion list. We already need to add an exclusions preference to replace the one in the .jscodehints file. If we detect a problem, we could automatically add the problem file to the one, single exclusion list. If the user has another reason to exclude a file, they would just add the exclusion to that same list.

That said, the good thing about a detectedExclusions list is that the user is not left guessing how the file got there. Sticking with detectedExclusions makes sense to me from that perspective.