Add support for `tsx`.

[basarat]

If a file belongs to a project that has tsx enabled then getOrCreateProgram will require https://github.com/fdecampredon/jsx-typescript/ instead of typescript.

Including @fdecampredon into the conversation by force mentioning 😛 ❤️. Just curious if we should expect the languageService to just work?

Refs : #56

[fdecampredon]

yup In fact I was able to use brackets-typescript with it :D, however the 'formatting' part won't work, I had to disable it, and you don't have completion on attributes due to microsoft/TypeScript#1947 and microsoft/TypeScript#1926