Remove worker tables

[MartinThoma]

Workers are only a special type of user.

Step 1

Get rid of wm_workers. Add the contents to wm_users?

Open questions:

• What to do with API_key?
  • Simply moving to password is not a good idea, as passwords might have duplicate entries
• What to do with url?
• How to save which user has which workers?

Step 2

wm_partial_answer and wm_worker_answers should get merged.

Step 3

Adjust view, e.g. http://write-math.com/view/?raw_data_id=330230