* Modified the WindowMessageSink to use an enum where possible.
* I managed to find more of the windows messages, and it was worth it. I expect that there is a bug, while currently two events aren't handled: WM_CONTEXTMENU & NIN_SELECT. Why can be read here: https://docs.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shell_notifyiconw. Also added NIN_KEYSELECT
* A small stability fix, although it most likely wouldn't happen that the MouseEventReceived isn't assigned it's done so in a different location and might hit us somewhere in the future. I also removed unneeded assignments.
* Applied some code conventions, used more current language features which should improve readability and making it easier to re-factor / modify. Also fixed some typos in documentation.
* Changes based on PR conversation for the SystemInfo
* Some modifications due to conversations on the PR, especially I removed the FlagsAttribute on the BalloonFlags.
* Removed Silverlight targeting in code.
