No more ambient modules for tns-core-modules/* subpackages.

- Use path mappings in tsconfig.json to resolve module typings
- Only use ambient mobules for global API's
- Move single-file modules to a subdir with the same name so that
we can provide a hand-written typing next to it (via package.json)
- Delete all mentions of tns-core-modules.d.ts
- Delete reference d.ts assembly build steps. Not needed anymore.
- HACK! Use a <reference> for global typings in application.d.ts
to avoid publishing a separate @types/tns-core-modules package.
- Rename declarations.d.ts to tns-core-modules.d.ts to preserve
JS project mappings in references.d.ts (the only place we use those)

tns-core-modules/image-source/image-source.ios.ts

@@ -1,7 +1,7 @@
 // Definitions.
 import { ImageSource as ImageSourceDefinition } from "image-source";
 import { ImageAsset } from "image-asset";
-import * as httpModule from "http";
+import * as httpModule from "../http";
 
 // Types.
 import { path as fsPath, knownFolders } from "file-system";
@@ -12,7 +12,7 @@ export { isFileOrResourcePath };
 let http: typeof httpModule;
 function ensureHttp() {
     if (!http) {
-        http = require("http");
+        http = require("../http");
     }
 }
 
@@ -239,4 +239,4 @@ export function fromFileOrResource(path: string): ImageSource {
         return fromResource(path.substr(RESOURCE_PREFIX.length));
     }
     return fromFile(path);
-}
+}