[Cashtab] Auto add latest commit hash to configure

Summary: Added latest commit hash to the footer of the configure.js component, links to latest commit on github. Related to task T1760.

Test Plan:
ensure cashtab is rebased with latest version of master
cd web/cashtab
npm start
in separate terminal run git rev-parse HEAD
take note of latest commit hash
ensure link on configure page matches latest commit hash

npm run extension
load extension
ensure link on configure page matches latest commit hash

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10431