Add method to set QTabBar Tab alignment

Qt stylesheets allow complete customization of the widgets including QTabBar. In some cases Tabs don't look like traditional tabs any more, which is the case with our application.

However, the QTabBar alignment is limited to native tab alignment i.e. Left on Windows and Middle on macOS. While its understandable to have that limitation when Native UI is being rendered, but in cases of custom styled QTabBar its a huge limitation. 

Proposed method:
void QTabBar::setAlignment(Qt::Alignment alignment);

Calling this method forces specific tab alignment i.e. Left, Center, Right.