- persist in videoencoderconfiguration
- restart server if necessary (kernel blocks access when streaming?)
- remove unsupported profile selection and allow quality 0,1 for vbr/cbr

Previously, some camera settings were persisted in v4l2ctl.json, but
others were not (either overwritten by subsequent actions or never
there in the first place).

This tries to make sure there's only one place we're storing
settings, and then makes sure to save them all. The
signal-exit package is introduced to more reliably handle
exit cleanups, which is now more important if the user
has just changed a setting (save runs on a 30 sec delay).

Also re-introduce H264 profile handling.