SVG images, forms, extension / helper methods and cleanups

- ADD: started to implement document class that handles data of a SVG
image incl. WPF control
- ADD: helper / extension methods and classes that make forms draggable
/ moveable
- CHG: code cleanups
- ADD: SendMessage() extension / helper method to directly send WndProc
messages to a form
minor changes
added IndexOf() helper and extension methods for sequences
fixes and extensions for IndexOf() helper / extension methods
removed overwritten IndexOf() helper/extension methods