Adds Frequency Offset option to adjust the vertical freq to captured frequency center#169

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jwcrawley wants to merge 2 commits intomiek:mainfrom jwcrawley:master

+85-13

Commits on Sep 3, 2020

added frequency offset feature to allow centering vertical graph around real captured frequency
jwcrawley
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readded minor lines and cleaned up commit prior to PR
jwcrawley
committed