Align DropDown content to left.
Align DropDown content to left.

Fixes #605.

AvaloniaUI/Avalonia,wieslawsoltes/Perspex,MrDaedra/Avalonia,Perspex/Perspex,SuperJMN/Avalonia,grokys/Perspex,MrDaedra/Avalonia,susloparovdenis/Avalonia,wieslawsoltes/Perspex,susloparovdenis/Avalonia,AvaloniaUI/Avalonia,OronDF343/Avalonia,Perspex/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,grokys/Perspex,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,akrisiun/Perspex,SuperJMN/Avalonia,OronDF343/Avalonia,jkoritzinsky/Avalonia,susloparovdenis/Perspex,wieslawsoltes/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,susloparovdenis/Perspex,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Perspex,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,jazzay/Perspex