[admin-theme] menu doesn't respect assigned permissions

[okraits]

The links "Templates" and "VPN Servers" are available in the menu although the user doesn't have the rights for these objects:

I had a look into this a bit:

https://github.com/openwisp/openwisp-utils/blob/master/openwisp_utils/admin_theme/context_processor.py#L32

• ModelAdmin.has_module_permission evaluates permissions only on the module level, not on the model level (Device, Template, Vpn).
• openwisp-utils is decoupled from the other OpenWISP modules so we don't have access to models etc

[nemesifier]

@okraits as we discussed, this may work:

1. get the list of permissions of the user (I suggest caching it)
2. build a list of strings, each string representing the app_label and the model name
3. when iterating over the models, we build the string with the app_label and the model name and we check if that string is present in the list built in step 2

[okraits]

@nemesisdesign I implemented a fix before I saw your comment 😀

I didn't find a different solution than the one I implemented. Please tell me what you think.