Add isIOS, isAndroid in platform, and fast ts watcher and transpiler

Image should not requestLayout when sized with 'exactly' spec

Update image tests

Tests will run in ios only

package.json

@@ -21,5 +21,10 @@
     "time-grunt": "1.3.0",
     "tslint": "3.4.0",
     "typescript": "1.8.2"
+  },
+  "scripts": {
+    "tsc-tiw": "node build/tsc-dev.js tiw",
+    "tsc": "tsc",
+    "link-tests": "cd tns-core-modules && npm link && cd ../tests && npm link tns-core-modules"
   }
 }