Support Appcompat and alert dialogs in the support library

[dabluck]

Android support library 22.1 update brought support for material dialogs in older apis.

see here: http://android-developers.blogspot.com/2015/04/android-support-library-221.html

It would be nice to be able to support in this library, but implementation is tricky because if the activity and theme aren't from appcompat then it will crash the app. obviously forcing all users to use appcompat isn't ideal.

Let me know your thoughts. the code for supporting only appcompat is trivial (see my fork if you want).