Fixed #22058 -- Refactored handler and created a generic mechanism to deal with server/client errors.

**What is done**:

- Refactored handlers into generic ones.
- Deprecated original default views.
- Added generic views.

**Improvements Required**:
- Docs build have several warnings due to removing original handlers.
- A writeup for new views.

**Suggestions**:
- We could add two generic exceptions also: `HttpClientException` and `HttpServerException` to add onto the functionality.

@timgraham 
I think we could mention why we are putting this here, i.e. if anyone tries to import them else it would seem strange to put something like this under backwards incompatible and might create confusion.
Or we could put it under a different section, that way users will be informed of the new way of working.

IMO, second option is better..what do you say as mostly people do not import this rather define their custom handers in `url_conf` and that is backwards compatible and this above note might confuse them.