Expand diagnostics

• updater
  • Include UCI config in diagnostics
  • Improve shell code
• os_release
  • Make it actually a module (it wasn't included)
  • Fix for latest OpenWrt release
  • Improve shell code
• messages
  • Shell refactoring
• dns
  • Fix shell quoting and output format
  • Update list of Turris domains
• notification
  • Add new module to create and send user notification
• certgen
  • Add new module to run Sentinel Certgen
• Run modules in given order by prepend their names with numbers

Fix #4 (closed)