Fix #617 Windows Desktop Region Record

Fix a small bug of in Desktop plugin for Windows.
Windows can record a region of desktop correctly now.
Related #576 High/Low DPI Adapting

The Qt UI would change the size according to the logical DPI of the computer
Only Windows and Linux have been tested. (Should also work on Mac but have not tested).
The function is unfinished.
Remove unused variable
Add the interlayer qt classes for auto dpi adapting