#1213 Integrate Promises to the language

Originally at 2015-12-09T22:12:16Z by Herbert Vojčík closed at 2016-02-07T15:01:43Z With `amber-compat-promise` to supply the polyfill. Since `fetch` returns a Promise, #1212 sort-of needs this. I'd say Amber should wrap `Promise` class, not just use it via JS proxy. That brings in the question, if Pharo or some other Smalltalk out there do have some kind of Promise/Future API which couls be used here.