Revert the change to attempt backward compatibility with Scrooge 2 scrooge-runtime. In order to ease the migration from Scrooge 2 to Scrooge 3, we now allow both versions to co-exist in user projects.
- The artifact ID of scrooge-runtime is changed to scrooge3-runtime.
- The content of scrooge-runtime is now split into two packages:
  com.twitter.scrooge.base contains ThriftStruct, ThriftStructCodec, ThriftEnum and ThriftMetaData
  com.twitter.scrooge.util contains Utilities, Option, ThriftStructSerializer

RB_ID=132086