Windows: Fix High DPI issues

Pending changes:

• Find out UI scale factor of Window: https://codereview.qt-project.org/#/c/87716/ for Windows 8.1 . No idea for Win7 yet, might have to check metrics before and after setting DPI awareness (see version 1 of that patch). Is this actually need; is there a point returning a DPR for a screen in case Windows does the scaling?

• Platform-independent scaling/Windows Proposal A) (Morten): https://codereview.qt-project.org/87985
• Platform-independent scaling/Windows Proposal B) (Paul) https://codereview.qt-project.org/#/c/90790/

• Fix windows style for scaling: https://codereview.qt-project.org/#/c/91451/

• Fix up QWizard: https://codereview.qt-project.org/#/c/91318/ Turns out custom margins are ok in DP, but the wizard elements are a total mess. Maybe just disable it for DPR != 2.

Things to do:

• Some machines fail to set DPI awareness: SetProcessDpiAwareness failed: "COM error 0x80070005 (Unknown error 0x0ffffffff80070005) (also observed in autotests when calling it repeatedly).

Various oddities:

• With a scale factor of 100%, setting DPI awareness to 0 does not have any effect. It defaults to 2.

Done changes:

• Use Win 8.1 API, make awareness configureable 2e44a9e4918cd6d9d7f33f61330c456249dd9b0f (30.4.2014, dev, 5.4) https://codereview.qt-project.org/#change,84355

• Fix QPA parameter checking: 800214f0b9cbbbc7b77a12180ce59033dd3cca64 (dev, 5.4) https://codereview.qt-project.org/#change,85380

• Add more cursor pixmaps depending on size : 7de95ede1bc542c329bf1d23633615693a04d14e (dev, 3.7.2014, 5.4) https://codereview.qt-project.org/#/c/88720/