Allow per-model permission level management

[zipavlin]

Description

This PR modifies advance permission managements so it is possible to set permission level per module, not only on global level. This is useful when there is no need for per-item management except for few specific modules, fe. pages where we want to allow users to edit only specific page(s).

This change should be backwards compatible and can be used by adding a level to twill.permissions.modules array:

'permissions' => [
    'level' => \A17\Twill\Enums\PermissionLevel::LEVEL_ROLE_GROUP,
    'modules' => [
        'pages' => \A17\Twill\Enums\PermissionLevel::LEVEL_ROLE_GROUP_ITEM,
        'posts'
    ]
]

Tests

I was not able to run tests on locale machine, but I did test it manually :)