Reduce dependence on web.py

Since we have a plan to move from web.py to pecan, it would be great if we incapsulate web.py-related things in some abstractions.

current state:

1/ We have a lot of response answers over the code, each of them directly depends on web.py (`web.notfound`, `web.badrequest`, `web.ok`, web.created and so on).

2/ We have a lot of HTTP exception catchers (`web.badreques`, etc) in out API handlers.

3/ We have a few places with direct access to raw POST data: `web.data`.

4/ We have a few places with direct access to formatted data: `web.input`

All these dependencies scattered all over the code, and should be incapsulated in some abstraction in the base class.