Remove unused classes and methods

[bcasey-zd]

• Remove “initializeForBigTableWrite()” from PipelineOps, this removes the dependency on BigTable and aligns us more closely with the Apache Beam API.
• Remove MiscOp entirely, the clue that this was becoming a kitchen sink dumping ground was in the name!
• Simplify Duration ops to just implicit conversion between Scala Duration/Java 8 and Joda. If you want the nice duration DSL (e.g “5 minutes”) this is already in the Scala Duration library, no need to reimplement
• Try / Option / Either coders:
  • Write/read marker byte directly
  • Better encoding id

@zendesk/zodiac @dasch