RFR: 7081: Update Copyright year to 2021, Validate and update license attributes [v4]

[Guru Hb]

> Updated Copyright year to 2021 for below 
> 1. License show in "About" dialog
> 2. Copyright year in License file 
> 3. Update site landing page 
> 4. added a helper script which can be used to update copyright year for modified git files.

Guru Hb has updated the pull request incrementally with one additional commit since the last revision:

  Removed hardcoded year value

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/190/files
  - new: https://git.openjdk.java.net/jmc/pull/190/files/96901546..b5a9536c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=190&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=190&range=02-03

  Stats: 16 lines in 1 file changed: 13 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jmc/pull/190.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/190/head:pull/190

PR: https://git.openjdk.java.net/jmc/pull/190