Context arguments handling refactoring

- Moved context class arguments setup back under the suite settings
- Extracted context creation logic into `ContextFactory`
- Added support for named context arguments

Basically, this PR adds full and equal support for next three setups:

```yml
default:
  suites:
    project:
      contexts:
        - VisitorContext
        - AdministratorContext
```

```yml
default:
  suites:
    cli:
      contexts:
        - CronContext:
            - 24
            - 13
            - 72
        - APIContext
```

```yml
default:
  suites:
    web:
      contexts:
        - VisitorContext
        - MinkContext:
            baseUrl: http://localhost
```