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
Do you think anyone is using it to exclude entire folders for performance? Doesn't hurt to leave it in.