backend: log exceptions as debug messages if the expection will still be raised

Useful to avoid showing the GUI debug panel when it's not needed.
driver simcam: use metadata for default exposure time

This allows to be directly a bit more realistic
gui menu: link new menu entries

link:
 * reset fine alignment
 * play/pause
 * auto bc
 * autofocus

Should work pretty well for all the tabs (and be disabled when needed)