Fix #614 Add video scaling options

Freeseer now supports converting video signals from one display
resolution to another. Technically we already supported this, but there
were no scaling options so it wasn't very useful.

The following scaling options are now available when recording video:

- No scaling
- 240p (320x240)
- 360p (480x360)
- 480p (640x480)
- 720p (1280x720)
- 1080p (1920x1080)
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.
Style fix
Add more classes into the dpi adapting set