Implement GetMenuPosition API.
Fix Mac compiler errors.
Add parentId as a required parameter of NativeMenuModel::setTag().
Merge branch 'rlim/menu-position-api' of https://github.com/adobe/brackets-shell into rlim/menu-position-api

Conflicts:
	appshell/native_menu_model.cpp
Making review comment changes.
Change return type to int32.
Merge pull request #182 from adobe/rlim/menu-position-api

Implement GetMenuPosition API for native menus unit test.