RFR: 7929: Add release splash for 8.3

[Marcus Hirt]

What it says.

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Commit messages:
 - 7929: Add release splash for 8.3
 - Merge branch 'master' into jmc8 in preparation for the 8.3 release.
 - 7877: Update the jmc version in jmc8 branch to 8.2.1
 - 7381: Better descriptions for reports
 - 7443: Wrong version in THIRDPARTYREADME
 - 7569: Improve the implementation of Twitter plugin
 - 7561: Update to the release splash screen for JMC 8.2
 - Merge branch 'master' into jmc8
 - 7436: Update version to 8.1.1 in the jmc8 branch
 - 7231: JMC createReport for JMC8 Automated Analysis fails to evaluate several rules
 - ... and 20 more: https://git.openjdk.org/jmc/compare/095d0687...70c4c3f9

Changes: https://git.openjdk.org/jmc/pull/441/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=441&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-7929
  Stats: 23 lines in 2 files changed: 23 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jmc/pull/441.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/441/head:pull/441

PR: https://git.openjdk.org/jmc/pull/441