Add framerate control to sherlock265

[EdenGottlieb]

This PR adds framerate control to sherlock265.

The framerate is controlled using a Qt SpinBox element.

Default framerate is 30, which is suitable for most videos but not all.

I tried extracting the video framerate from the SPS, which is analyzed inside libde265 internals, but is not readily accessible from outside. The only option appears to be to dump the whole SPS header and process it manually, or modify libde265 to provide it with the API, which is a bit out of scope right now.

Further work:

• Detect video framerate automatically