[e.cash] Play animations on mining and staking only once

Summary: Making animations on /mining and /staking to play only once because they do not have a closed loop, leading to jumpy animations. /index needed to be changed to make it work. Added NoLoop param as a new option for image animations.

Test Plan: visit e.cash/mining and e.cash/staking and see if animation plays only once. Check out other animations on the page to double check they are not affected by this change.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Subscribers: Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D16524