Added ShowInTaskbar/NoActivate and made IsClickable non-static

[iXab3r]

Hey! Thank you for the great library.

Several changes

• Changed approach with IsClickable a bit - I needed to mutate styles for other properties, so made it so it respects current set of styles and not just overrides it
• Added two new properties
• • ShowInTaskbar - controls styles so that OSD window gets hidden from the taskbar.
• • NoActivate - controls styles and changes WndProc processing a bit so that if enabled, the window DOES NOT steal focus from the window when activated (in the demo note how title bar color changes = focus changes). This is especially useful for games as allows to have non-interceptive overlay with some settings, etc. Known issue - textboxes require constant focus to work. So if you want users to type in something, you will have to dynamically enable activation. For all other types of controls I did not notice any issues.

EyeAuras_tyGzRCiFS90rBO4v.1.mp4

[jackburkhardt]

I was just about to implement this myself before finding this PR. These properties are supremely useful for games. @zaafar do you still have the bandwidth to roll these changes in?