[Sprint/QA] (fix): replaced play store link to minds.com/mobile
requested to merge eiennohi/engine:sprint/QA.fix.welcome-email-template-has-link-to-play-store into master
closes #216 (closed)
depends on front!118 (merged) , which has the image asset for the Minds Android App. @markeharding, please let me know if you want me to cherry-pick that asset onto a different merge request.