[cashtab-components] Replace all instances of CashTab with Cashtab

Summary: Replaced all instance of CashTab with Cashtab in cashtab-components. Related to task T2537.

Test Plan:
cd web
grep -r 'CashTab' cashtab-components/ should return no results

cd cashtab
grep -r 'CashTab' extension/ should return no results (excluding files in dist dir)

Then:

cd web/cashtab
npm run extension
confirm that clicking on a cashtab badge button still opens the extension

cd web/cashtab-components
npm run storybook
Confirm that storybook runs

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11731