Libadwaita style

[DeltaCopy]

@testlab833

(brought this up elsewhere think it deserves a separate issue)
Some have asked to port this theme to gtk, but I'd propose, instead, porting gnome's style over to qt.

In addition to not splitting concerns between two completely different toolkits, this gets around all the problem of trying to theme apps that are engineered to prevent themeing. It will also allow qt apps to fit in well on Gnome which would be ... huge, to put it mildly. It's absurd that there is still no way to reliably make all apps look the same on Linux and the only way to do it is to create a libadwaita style for qt.

[testlab833]

@DeltaCopy thanks for creating the discussion topic. Regarding the scope, it seems that creating a gtk version is even more out of scope for a qt style as its a completely different platform and one which makes themeing difficult by design.