titlebar enhancement etc...

- minor documentation, removing unused stuff...
- title/titlebar visibility stuff
  - Right clicking anywhere causes window popup to appear #1409 
  - Hiding the minimimze/maximize/close buttons when `ShowTitleBar = false`, yay or nay? #1329 
  - WindowsCommands gone without ShowTitlebar? #1328 
  -  When ShowTitleBar=False, title bar buttons missing + cannot resize / maximize correctly #1172 
  - ShowTitle=False, Title-less window will drag but shows system default context menu #1391 
- show the system menu on
  - icon
  - if mouse yPos <= TitlebarHeight
  - UseNoneWindowStyle = true
- introduce ```ShowSystemMenuOnRightClick``` default to ```true```
- introduce ```ShowWindowButtonCommandsOnHiddenTitleBar``` default to ```true```

Closes #1409 
Closes #1329 
Closes #1328 
Closes #1172 
Closes #1391