Update Import transaction's UI

[jeesunikim]

• Don't skip "Sign" step on behalf of user when imported transaction has a signature. Previously, we skipped it to Submit so that its signature can be verified first; however, it's too much of handholding. Instead, display a Signatures table in Sign transaction and let them decide
• Submit transaction's details to include signature verification
• Sign transaction to include decoded XDR in JSON (included a language dropdown to switch JSON <> XDR)
• Replaced "unrecognized signers" (multisig that can't be verified offline) with "Existing signer (unverified)"

This needs more design feedback, especially around how to show existing Signatures on "Sign transaction" step

TX samples:

• tx with no signatures: AAAAAgAAAADSBFf5wA+BWEc1jDmwvbVupg1OrohBSRvHtEUG0FmTSwAAAGQAJoazAAAAFgAAAAAAAAAAAAAAAQAAAAAAAAABAAAAALeAVmIAOom1tFe0PE2ZHWOn+hSTZuYY136c6XpoWKBVAAAAAAAAAAAC+vCAAAAAAAAAAAA=
• tx with multisig as a source within operation: AAAAAgAAAADSBFf5wA+BWEc1jDmwvbVupg1OrohBSRvHtEUG0FmTSwAAAGQAJoazAAAAFgAAAAAAAAAAAAAAAQAAAAEAAAAAeH8YX2LLiZESynVxH8gRYbkGo9kp9WvTIKpupYBaGOwAAAABAAAAALeAVmIAOom1tFe0PE2ZHWOn+hSTZuYY136c6XpoWKBVAAAAAAAAAAAC+vCAAAAAAAAAAAGAWhjsAAAAQH33HKhPjIpWCuTTg0UwM2za+/cipMaDdrFliHBTmRcNRck0XW3Y5AYY4xu2+u/cUEzShd+1V2b7sRZdO8adGwg=
• tx with multisig: AAAAAgAAAADSBFf5wA+BWEc1jDmwvbVupg1OrohBSRvHtEUG0FmTSwAAAGQAJoazAAAAFwAAAAAAAAAAAAAAAQAAAAAAAAABAAAAACHl1hdsb68IKFCwYxh+DyTYAFNPPQYeXIdl3VD5t/10AAAAAAAAAAAC+vCAAAAAAAAAAAGAWhjsAAAAQHj3NcCOYERqouBvL0Uv3rQ91qNkxi0H28W9g2d8MA4pRAjzU9q1v3mDsiA3EJMaxMhyy4JISzC8OXkqBiqNJQI=
• tx with all required signatures: AAAAAgAAAADSBFf5wA+BWEc1jDmwvbVupg1OrohBSRvHtEUG0FmTSwAAAGQAJoazAAAAFgAAAAAAAAAAAAAAAQAAAAEAAAAAeH8YX2LLiZESynVxH8gRYbkGo9kp9WvTIKpupYBaGOwAAAABAAAAALeAVmIAOom1tFe0PE2ZHWOn+hSTZuYY136c6XpoWKBVAAAAAAAAAAAC+vCAAAAAAAAAAAKAWhjsAAAAQH33HKhPjIpWCuTTg0UwM2za+/cipMaDdrFliHBTmRcNRck0XW3Y5AYY4xu2+u/cUEzShd+1V2b7sRZdO8adGwjQWZNLAAAAQJ+YFFwUakiYWFhB2jKpXcLRTx0cbhni+6in7ui/vsZ037XGCUq9nm2yjNSamzO00qEvkGoKpAEKdpSTnakIDwM= (skips to submit)

⚠️ Design input needed:

• how to display <Signatures/> in sign step:**

• Multisig messaging:

Screenshots:

• "Sign transaction" step to include decoded details

• "Submit transaction" step to include verified signature

[stellar-jenkins-ci]

Preview is available here:
http://laboratory-pr2149.previews.kube001.services.stellar-ops.com/

[stellar-jenkins-ci]

Preview is available here:
http://laboratory-pr2149.previews.kube001.services.stellar-ops.com/