<EnableDefaultItems>false</EnableDefaultItems> along with
<Compile Include="**\*.cs" Exclude="obj\**" /> and <None Remove="**\*.cs" />
is needed, though.
Annoyingly we need to have two separate projects in two separate directories,
since Framework WPF projects aren't supported in sdk-style csprojs. The
Framework and Core projects also stamp over each others' bin and obj
directories, even if you set IntermediateFilePath, hence the need to put
them in entirely separate places
CommandBinding isn't a DependencyObject, so we can't get its DataContext
or View.ActionTarget -- we can only use the
IRootObjectProvider.RootObject. This should be good enough for most cases,
as these tend to get installed at the root of a window.
Fixes#50