RFR: Clarifications and other changes

[Jesper Wilhelmsson]

Several unrelated commits here, but each diff should be straight forward on its own.

1. Fixed the commit message in the backout example to actually follow the structure described in that section.
2. A large part of the introduction was lost in the split into one file per chapter. Restored.
3. Added some more info to clarify the Author role and how to request it.
4. Added a small section describing the webrevs and the cr.openjdk.java.net server.
5. Removed the old files that hadn't been included into the guide earlier - the webrev and cr.ojn stuff was the last pice of info   missing from  those files.

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Commit messages:
 - Remove obsolete files
 - Webrevs and cr.ojn
 - Clarified Author role
 - Restored the OpenJDK section
 - Fixed commit message

Changes: https://git.openjdk.java.net/guide/pull/86/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=86&range=00
  Stats: 281 lines in 7 files changed: 88 ins; 188 del; 5 mod
  Patch: https://git.openjdk.java.net/guide/pull/86.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/86/head:pull/86

PR: https://git.openjdk.java.net/guide/pull/86