WPF-based GUI runner

Added first run of the WPF-based GUI runner for Pickles.  No validation
or styling.  Very bare-bones.  Also upgraded some NuGet packages
Quick validation fix
Resharper settings
Add MahApps
Include mahApps in project file
Rework main window
Merge pull request #82 from dirkrombauts/gui

Gui Rework
Updated NuGet to latest version because of error on build
Switching to Green
Merge pull request #83 from dirkrombauts/gui

Going Green
Added a textbox for output messages from Pickles
More commits for the text box
A collection with support for multiple selection
More options in the relaycommand
Rework of the UI and its ViewModel
Save last used paths to a settings file
Merge pull request #95 from dirkrombauts/gui

Gui updates
Adding validation to the screen
Removing IDataError stuff
Merge pull request #99 from dirkrombauts/gui

Gui: validation checkboxes