I created a class library which is contained of WPF Windows and some user controls inherited from my c# classes that helps me to customize certain wpf controls.
Now
If you can't find the Resource Dictionary (WPF) file type when trying to create the dictionary, do this:
Add the following line to your project file (.csproj), into the first <PropertyGroup>
element:
<ProjectTypeGuids>{60dc8134-eba5-43b8-bcc9-bb4bc16c2548};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
Reload the project. Now you should have all the item types that can be found in a normal WPF project, including the Resource Dictionary (WPF).