Move common method for a CapsuleManager to trait, this would reduce the ...

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | None
| License       | MIT
| Doc PR        | None

* Move common method for a CapsuleManager to trait, this would reduce the requirement to produce new CapsuleManager for other component in the future (e.g: laravel/framework#5032)
* Also remove duplicate "require-dev" component (when already explicitly declare in "require").

Ahh, I see...