Change from "classic" TS 1.6 imports to the default resolution scheme.

- Use relative imports in place of most of our absolute ones.
- Add "private" ambient modules for modules that we need to import using
an absolute path (e.g. when app/.../test-something.ts needs to import
ui/styling/style-scope)

http/http-request.d.ts

@@ -1,5 +1,7 @@
 //@private
 
-import http = require("http");
+declare module "http/http-request" {
+    import http = require("http");
 
-export declare var request: (options: http.HttpRequestOptions) => Promise<http.HttpResponse>;
+    export var request: (options: http.HttpRequestOptions) => Promise<http.HttpResponse>;
+}