Users with no view rights on the TaskManager space has broken task macro

[abrassat]

Describe the bug
Users who don't have view rights on the TaskManager.SkinExtensions page have broken css for task macros and the checkbox doesn't work.

Steps to reproduce
Steps to reproduce the problematic behavior:

1. Deny view rights for the TaskManager space for a user (call him DenyRightsUser)
2. Add a task macro to the Sandbox page
3. Log in as DenyRightsUser, and view the Sandbox page
   This also happens if you deny the rights for an entire group of users.

Expected behavior
The task macro is properly displayed, and the user can click the checkbox to update the status of the task.

Actual behavior
The task macro css and js is not loaded, breaking some of the functionality of the task macro.

Screenshots
Broken css look:

Environment (please complete the following information):

• OS: linux mint
• Browser firefox
• XWiki version 15.10
• App version 3.11.0

Additional context
Denying view rights for the entire TaskManager space can happen in the case when you want to deny the creation of new tasks from the template (see #122 and #263 for related issues). The point is that it's easy to deny view rights for technical TaskManager pages by mistake.

An improvement for this could be to move all technical pages into their own TaskManager.Code space, and explicitly allow view rights on that space for all users, to avoid potential mistakes.