Change management of tasks statuses

[GoogleCodeExporter]

Remove fields `accept_date` and `status` from table `task`. Add new table 
`tasks_status` which is to has following fields:
1. `id` (type integer, primary autoincremented key)
2. `task_id` (type integer, not null foreign key to `task`.`id`)
3. `status` (type integer, not null value, list of possible values see below)
4. `date` (type date, not null)

Possible values of status:
1. NEW[open]
2. ACCEPTED[open]
3. STARTED[open]
4. RENEW[open]
5. DONE[open]
6. CANCELED[close]
7. APPROVED[close]

Original issue reported on code.google.com by yermoche...@gmail.com on 10 Jun 2015 at 10:09