tvheadend: multiple improvements

tvheadend: multiple improvements
- Added menuconfig options:
  - TV sources and protocols: SAT>IP, IPTV, HDHomeRun
  - SoftCAM (3 options)
  - Image cache (default changed to OFF)
  - Trace debug option (default changed to OFF)
- Added menuconfig descriptions.
- Removed codecs.
- Made PIE option dependent on global OpenWRT PIE setting.
- Run as regular user, not root.
- Added USB hotplug script to change DVB tuners permissions.
- Fixed a first-start bug(?) that I encountered: admin account created but not saved.

Signed-off-by: Marius Dinu <redacted>