OrmLite interfaces added to iOS project

Since System.Data & System.ComponentModel.DataAnnotations are now
available in Xamarin.iOS we can enable these interfaces.

OrmLite now has iOS solution and the base project. I will see if I can
add SQLite and SQLCipher as database providers for iOS (and Android).
Merge pull request #823 from sami1971/master

OrmLite interfaces added to iOS project