Use better names for Linux screen capture sources

build/data/obs-plugins/linux-xcomposite/locale/en-US.ini

-XCCapture="Xcomposite Capture"
+XCCapture="Window Capture (Xcomposite)"
 Window="Window"
 CropTop="Crop Top (pixels)"
 CropLeft="Crop Left (pixels)"

build/data/obs-plugins/linux-xshm/locale/en-US.ini

-X11SharedMemoryScreenInput="X11 Shared Memory Screen Input"
+X11SharedMemoryScreenInput="Screen Capture (XSHM)"
 Screen="Screen"
 CaptureCursor="Capture Cursor"