Normal Modes - Publish 1.0

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From the PhET Project Overview spreadsheet, the milestones for this epic are:

2021 Q1 team = @issamali67, with support from @pixelzoom

Milestone	Start	End
Review and Finalize Design	02/01/21	02/28/21
Dev to Feature Complete	01/01/21	05/31/21
Interviews	06/01/21	06/15/21
Code Review, QA, Published	06/01/21	07/25/21

@issamali67 FYI, so that you're aware of the milestones.

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4/8/21 Q2 planning meeting:

This epic is deferred, and will likely not be included in Q2 work. @kathy-phet and @issamali67 will stay in touch.

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Title of this issue changed to "Normal Modes 1.1 release". The prototype released in #64 uses the 1.0 branch.