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/css-value/reworkcss-value.d.ts

@@ -1,10 +1,8 @@
-declare module "css-value" {
-    interface CSSValue {
-        type: string;
-        string: string;
-        unit?: string;
-        value?: number;
-    }
-
-    export function parse(cssValue: string): Array<CSSValue>;
+interface CSSValue {
+    type: string;
+    string: string;
+    unit?: string;
+    value?: number;
 }
+
+export function parse(cssValue: string): Array<CSSValue>;