Add option to disable bringing Qt Creator on top after successful build

There is a QApplication::alert call after each build. It places Qt Creator above all other windows (at least on Linux Mint). It even changes current desktop!

Pretty often i switch to other windows after launching build process (especially for large projects). So unexpected apperaing of Qt Creator's window causes some inconvinience. I can't remember how much times i accidently closed it or started typing in wrong window.

Making this QApplication::alert call configurable by user in settings should fix this problem.

There are also QApplication::alert calls in debugger and valgind plugins. I suppose that new option should affect them too.