Add collaborators to app

[icyleaf]

Refer to the simplest member management implemented in AppCenter.

Todo list:

• [x] db design
• [x] app collaborator management
• [x] new permission
  • [x] dashboard page
  • [x] apps page
  • [x] debug files page
  • [x] teardown page
• [ ] collaborator control in Admin's users
• [ ] app's collaborators APIs
• [x] update document https://github.com/tryzealot/docs/pull/79

Relates to #1494