[cashtab] Success modal animation edits

Summary:
Modifying the success modal styles and animation to be hopefully a bit more refined

• adjusted timing
• removed the progress bars and added a little exit "burst" to the checkmark instead
• simplified the modal content. Since the modal is only visible for just a moment. I thought the txid and copy button were not really practical. So simplifying to just a link to open the tx

Best way to compare is test it out in master and then in this branch to see if these adjustments feel better, as its pretty quick

Test Plan: preview and check. Send a tx using the url generated send (ie: /#/send?bip21=ecash:.....)

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18695