[GOBBLIN-543] Opensource StandardManifestRecord and DistributedClassp…

[zxcware]

…athManager

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [x] My PR addresses the following Gobblin JIRA issues and references them in the PR title.
  • https://issues.apache.org/jira/browse/GOBBLIN-GOBBLIN-543

Description

• [x] Here are some details about my PR:
• StandardManifestRecord: A standard representation of a record from a service that gobblin reads or writes
• DistributedClasspathManager: A class to add artifacts to the classpath of an MR job

Tests

• [ ] My PR adds the following unit tests:
• DistributedClasspathManagerTest
• Live job test in progress...

Commits

• [x] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"