Implement recovery flow

[jeffgca]

Users of apps created with this template should be able to export a recovery kit that can be used to recover their account in the case that all linked devices are logged out or unrecoverable.

Tasks

• [x] Get Webnative refactor tested, approved and merged
  • https://github.com/fission-codes/webnative/pull/432
• [x] Upgrade to Webnative 0.35
• [x] Add recovery kit
• [x] Determine boundary between WAT and webnative for recovery pieces (some initial thoughts)
• [x] Add filesystem recovery
• [x] Add username support for filesystem recovery

[jeffgca]

This is blocked in improvements to the new fission server.