SelectDirectoryService.InitialDirectory property fixed.
changed strategy of using SelectedPath and RootFolder
removed unused variable InitialDirectory
changed usage of the variable initialDirectory
Merge remote-tracking branch 'origin/develop' into develop

Conflicts:
	src/Catel.MVVM/Catel.MVVM.Shared/Services/SelectDirectoryService.cs
Merge pull request #37 from Khomutov/develop

SelectDirectoryService.InitialDirectory property fixed.