Update the Still Export UX

Being able to export stills from Color is a great feature. When dealing with a large number of stills, the process could use some basic enhancements:
- Show a progress bar for the stills export process. Currently there is zero UI for it, and the only way to know it's happening is that you can't access the Resolve interface until it finishes.
- Allow us to cancel the export. Again, when exporting a large number of stills, pressing Escape does nothing, and you have to wait until the export process has finished.
- Exclude .drx on export - even when you choose a different format (say PNG) it will export the DRX file along with it, so you end up with a bunch of duplicate stills.
- Add the ability to export stills to the Edit and Cut pages as well - allow the process to work on Timelines or Bins.
Edit: - Add the ability to only export .drx
- Show a progress bar for the stills export process. Currently there is zero UI for it, and the only way to know it's happening is that you can't access the Resolve interface until it finishes.
- Allow us to cancel the export. Again, when exporting a large number of stills, pressing Escape does nothing, and you have to wait until the export process has finished.
- Exclude .drx on export - even when you choose a different format (say PNG) it will export the DRX file along with it, so you end up with a bunch of duplicate stills.
- Add the ability to export stills to the Edit and Cut pages as well - allow the process to work on Timelines or Bins.
Edit: - Add the ability to only export .drx