Blender Git Loki

UI: Correct the text alignment in the quick setup (splash screen) dialog

The "quick setup" dialog is actually a 'menu', and the "splash screen" block
contains the UI_BLOCK_LOOP flag which causes the buttons' text to align
to the left, however, usually regular buttons have centered text.

As a workaround, add the UI_BLOCK_QUICK_SETUP flag which prevents
the text from being left-aligned.

Differential Revision: https://developer.blender.org/D10486

Reviewed by: Julian Eisel