RFR: 6960: Update Copyright year and Welcome page

[Guru Hb]

Fix contains : 
1. Updating Copy right year 
2. Copyright notice should now show "All rights reserved." (Text shows in JMC application -- About box, License detail etc.. and not in the source header). 
3. JOverflow was listed as addition / optional plugin , which is not true any more as it is distributed along with jmc product. 
4. Few html page had missing "JDK" prefix for "mission control". which is now shown as "JDK mission control" instead of "mission control"

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Commit messages:
 - wqUpdated Copyright year and its text
 - 6960: Joverflow listed as install-able plug-in

Changes: https://git.openjdk.java.net/jmc/pull/149/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=149&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6960
  Stats: 121 lines in 39 files changed: 0 ins; 43 del; 78 mod
  Patch: https://git.openjdk.java.net/jmc/pull/149.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/149/head:pull/149

PR: https://git.openjdk.java.net/jmc/pull/149