Added DataAnnotationsModelMetadataProvider to fix issue with display attribute not being displayed in mvc view

Fixed required and string length attributes so that they they generate client side validation in mvc views.
Fixed issue in post build where manifest is not deleted if there is an exception in post build execute.

Added functionality to transform view model annotations using regex, from [Display(Name = "Test1", Prompt="Test2", ShortName="Test3")] to [Display(_("Test1"), _("Test2"), _("Test3"))] so that the annotations can be processed by xgettext, after which point the annotations are restored to their original values.