permission management

[cornernote]

• module should have global permission (can view, can update)
• each panel should also have its own permissions (can view, can update)

[uldisn]

I started implementing access control:

• admin role
• dashboard view roles
• panel view roles

https://github.com/uldisn/yii2-dashboard

[cornernote]

I'm not using this anywhere in production at the moment, but I plan to later.

Feel free to send a PR and I'll pull in what you have done.