RDISCROWD-6222 Show GIGwork users why no tasks are available

[peterkle]

Issue number of the reported bug or feature request: #RDISCROWD-6222

Describe your changes
As a user, I would like to be able to see why no more tasks are available to me even when a project is not yet completed, so that I can understand if there is a problem with the project or if I can work on more tasks.

A typical cause for this is that the project is using the User Preference or Task Queues scheduler and the remaining tasks have preferences configured that are different than the user's.

Notes

• Notice that I refactored the "redirect_to_password" check by moving it earlier in the function to avoid needless computation of metrics. This change is unrelated to this feature.
• JSON body shape:

  "notifications": {
    "project_incomplete_info": {
      "user_preferences": {
        "account_profile_link": "/account/user/", 
        "task_scheduler": "User Preference Scheduler"
      }
    }
  }

[coveralls]

Pull Request Test Coverage Report for Build 5717682690

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 94.127%

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Totals
Change from base Build 5648206489:	0.003%
Covered Lines:	16924
Relevant Lines:	17980

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💛 - Coveralls

[kbecker42]

Thank you.

[kbecker42]

# Task Queue scheduler: verify notification message displays.

Also, is this updating the project repo and saving the new task queue preference via self.app_get_json(url)?

[peterkle]

self.app_get_json(url) is a test helper which only fetches data. The update to project scheduler is done via assignment in project.info['sched'] = Schedulers.task_queue

[XiChenn]

lgtm

[XiChenn]

Feel free to "Squash and merge" upon all checks passed. You will also need to update the "pybossa-default-theme" pointer as it is merged to the main branch the hash could be different.