Rename FluentSiteMapCreator.cs.pp to *Initializer.*

Step 1 of renaming the class (and its single method)
Rename FluentSiteMapCreator class to *Initializer

Also renamed the PostStart to Initialize
Update Sample proj to match Initializer rename in pkg

Need one more commit to update content of FluentSiteMapInitializer.cs
Rename FluentSiteMapCreator to *Initializer in Sample

To match package