Add Low and Realtime priority options

For command-line use, priority IDs have changed. Check ReadMe.

Realtime will only work if program is started as Admininstrator. Else, the Realtime option will work the same as High.

Stores last minimized state

[new] Settings file loading and saving is now managed in its own class;
[new] Stores the minimized state. Closing the app from the tray will open it up already minimized in the tray the next time;

[fix] Command-line arguments can still be used, but the settings file will be used anyway to load the minimized state. Before it would ignore the settings file completely if there were command-line arguments.

First Release

v1.0

Add screenshot to readme