RFR: Reworked guide organisation

[Jesper Wilhelmsson]

This change was proposed in the mailing list and the replies were positive to the organization. No changes have been made to the content of the sections. The new index looks like this:

- Introduction
  - I have a patch, what do I do?
    1. Sign the OCA
    2. Socialize your change
    3. Find a sponsor
    4. Create a tracking issue in JBS
    5. Get acquainted with local process
  - Why is my change rejected?
- Mailing Lists
  - Changing your email address
- Repositories
  - Terminology and Naming Scheme
  - Installing and Configuring Mercurial
  - Cloning
- Code Conventions
- JBS - JDK Bug System
  - Filing a Bug
  - How to fix an incorrect backport creation
  - Resolved - Incomplete
  - JBS Label Dictionary
- Fixing a Bug
- Testing the JDK
  - JTReg
    - Running OpenJDK JTReg Tests
  - GTest
    - Running OpenJDK GTests
  - Excluding a Test
    - ProblemListing jtreg tests
    - Exclude jtreg tests using @ignore
    - Dealing with JBS bugs for test exclusion
- Producing a Changeset
  - Setting a JDK User Name
  - Creating
  - Merging
  - Pushing
  - Backing Out a Change
    - How to work with JBS when a change is backed out
    - How to work with mercurial when a change is backed out
- Code Owners
  - Area mailing lists
  - Directory to area mapping
- About this Guide
- Glossary

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Commit messages:
 - Reworked guide organisation

Changes: https://git.openjdk.java.net/guide/pull/39/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=39&range=00
  Stats: 1499 lines in 1 file changed: 697 ins; 705 del; 97 mod
  Patch: https://git.openjdk.java.net/guide/pull/39.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/39/head:pull/39

PR: https://git.openjdk.java.net/guide/pull/39