Add view decorators for checking membership, authorship and admin rights

The view decorators are used to check if a user is a member of a community, admin of the community and/or author of such models as Resource, CommunityPage, etc.
For instance, to make a change to a model instance, the user should be a member of the community and have the specific permission, so the following decorators will be used in combination with `permission_required`.

Dependent on #9 (models) and #15 (`mock` dependency should be moved to `requirements-dev.txt`).
You are right, the comma and a space aren't the right way to do it.
According to [PEP8](http://legacy.python.org/dev/peps/pep-0008/#indentation) (scroll a bit down to the list examples) the closing bracket in a multi-line construct should be placed on a new line.
Which one will work for us? 
```python
mockup_tests = [
    {"user": self.auth_user_foo, "success": True},
    {"user": self.auth_user_bar, "success": False},
]
```
Or maybe leave it this way?
```python
mockup_tests = [{"user": self.auth_user_foo, "success": True},
                {"user": self.auth_user_bar, "success": False}]
```
Usually the comma is left out there, in case a developer will append to the list and it is a good practice to prevent future accidental syntax errors. But if you consider the list will never be updated, I will remove the comma :)