Review and refactor e2e tests

[slaweet]

Lisk Nano has too many e2e tests. The number should be reduced through several strategies:

• Sometimes two e2e tests can be merged, e.g.
  https://github.com/LiskHQ/lisk-nano/blob/34978fd1376ae01008fbde4e4fe01951b3f93bcb/features/voting.feature#L1-L12
• Some are already covered by unit tests, thus can be removed, e.g:
  https://github.com/LiskHQ/lisk-nano/blob/34978fd1376ae01008fbde4e4fe01951b3f93bcb/features/send.feature#L18-L23
• Some should be converted to integration tests. For the sake of this issue, I would just mark them with @integration tag and there will be another issue to do the job after Pilot integration tests #733 is done. E.g.:
  https://github.com/LiskHQ/lisk-nano/blob/34978fd1376ae01008fbde4e4fe01951b3f93bcb/features/menu.feature#L84-L88

Appart from that, features/menu.feature is too big and not really just one feature. It should be split into multiple files: registerDelegat.feature, registerSecondPassphrase.feature signMessage.feature, verifyMessage.feature