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

Tue Jan 12 14:53:57 UTC 2021

On Thu, 7 Jan 2021 04:39:06 GMT, Guru Hb <ghb at openjdk.org> wrote:

> 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.

Pinged @guruhb about not hardcoding the from year in the copyright updating script - he'll said he'll fix before pushing.

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