XD-1178 Make avro sink options consistent with hdfs

Additional changes for this merge:
  - options.batchSize.description changed
  - timeoutOnIdle set to true for SimpleMessageStore

Squashed commit of the following:

    XD-1178 Make avro sink options consistent with hdfs
    - adding avro.properties with default values

    XD-1178 Make avro sink options consistent with hdfs
    - changing basePath to directory

    XD-1178 Make avro sink options consistent with hdfs
    - provide temporary custom implementation for DatasetTemplate
      to allow for null values in POJOs written (SHDP-245)
    - fixing avro sink expiration of groups