Modernize LoKiTrigger

• remove commented-out code
• prefer override over virtual
• do not explicitly disable default constructors which are not implicitly generated
• do not add explicit trivial default constructor if the implicit one is generated and is equivalent
• do not explicitly call default constructors
• return concrete type from log_, cache_
• avoid a redundant if by changing add signature
• add UNLIKELY hints
• prefer boost::optional over construction with explicit bool
• remove trivial destructors
• prefer direct member initialization
• remove SVN keywords
• prefer auto