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)

text/span.ios.ts

@@ -1,4 +1,4 @@
-import spanCommon = require("text/span-common");
+import spanCommon = require("./span-common");
 import enums = require("ui/enums");
 import formattedString = require("text/formatted-string");
 
@@ -75,4 +75,4 @@ export class Span extends spanCommon.Span {
             });
         }
     }
-}
+}