RevitAddInUulity.dll can be found Revit installation folder. Note, Revit 2014 doesn't contain the Program folder. In my side it is located in C:\Program Files\Autodesk\Revit Architecture 2014
In Revit 2014 SDK in the Revit product installer, cannot find the AddinManager. However I can use the Revit 2013 version. Just change the addin manifest file, and copy to the folder for Revit 2014.